learn nodejs in 1 day: complete node js guide with examples

LearnNodeJSin1Day

ByKrishnaRungta

Copyright2016-AllRightsReserved–KrishnaRungta

ALLRIGHTSRESERVED.Nopartofthispublicationmaybereproducedortransmittedinanyformwhatsoever,electronic,ormechanical,includingphotocopying,recording,orbyanyinformationalstorageorretrievalsystemwithoutexpresswritten,datedandsignedpermissionfromtheauthor.

TableOfContent

Chapter1:Introduction

1. Whatisnode.js2. WhyuseNode.js3. FeaturesofNode.js4. WhentouseandnotuseNode.js

Chapter2:Download&InstallNode.js

1. Howtoinstallnode.js2. Installingnodethroughapackagemanager3. RunningyourfirstHelloworldapplicationinNode.js

Chapter3:Modules

1. WhataremodulesinNode.js2. UsingmodulesinNode.js3. CreatingNPMmodules4. Extendingmodules5. PublishingNPMModules6. Managingthirdpartypackageswithnpm7. Whatisthepackage.jsonfile

Chapter4:CreateServerandGetData

Chapter5:Node.jswithExpress

1. WhatisExpress.js2. InstallingandusingExpress3. WhatareRoutes4. SampleWebserverusingexpress.js

Chapter6:Node.jswithMongoDB

1. Node.jsandNoSQLDatabases2. UsingMongoDBandNode.js3. HowtobuildanodeexpressappwithMongoDBtostoreandservecontent

Chapter7:Promise,Generator,EventandFilestream

1. Whatarepromises

2. Callbackstopromises3. GeneratingpromiseswiththeBlueBirdlibrary4. Creatingacustompromise5. Callbacksvsgenerators6. FilestreaminNode.js7. EmittingEvents

Chapter8:TestingwithJasmine

1. OverviewofJasminefortestingNode.jsapplications2. HowtouseJasminetotestNode.jsapplications

Chapter1:Introduction

Themodernwebapplicationhasreallycomealongwayovertheyearswiththeintroductionofmanypopularframeworkssuchasbootstrap,AngularJS,etc.AlloftheseframeworksarebasedonthepopularJavaScriptframework.

Butwhenitcametodevelopingserverbasedapplicationstherewasjustkindofavoid,andthisiswhereNode.jscameintothepicture.

Node.jsisalsobasedontheJavaScriptframework,butitisusedfordevelopingserver-basedapplications.Whilegoingthroughtheentiretutorial,wewilllookintoNode.jsindetailandhowwecanuseittodevelopserverbasedapplications.

Whatisnode.jsNode.jsisanopen-source,cross-platformruntimeenvironmentusedfordevelopmentofserver-sidewebapplications.Node.jsapplicationsarewritteninJavaScriptandcanberunonawidevarietyofoperatingsystems.

Node.jsisbasedonanevent-drivenarchitectureandanon-blockingInput/OutputAPIthatisdesignedtooptimizeanapplication'sthroughputandscalabilityforreal-timewebapplications.

Overalongperiodoftime,theframeworkavailableforwebdevelopmentwereallbasedonastatelessmodel.Astatelessmodeliswherethedatageneratedinonesession(suchasinformationaboutusersettingsandeventsthatoccurred)isnotmaintainedforusageinthenextsessionwiththatuser.

Alotofworkhadtobedonetomaintainthesessioninformationbetweenrequestsforauser.ButwithNode.jsthereisfinallyawayforwebapplicationstohaveareal-time,two-wayconnections,whereboththeclientandservercaninitiatecommunication,allowingthemtoexchangedatafreely.

WhyuseNode.jsWewillhavealookintotherealworthofNode.jsinthecomingchapters,butwhatisitthatmakesthisframeworksofamous.Overtheyears,mostoftheapplicationswerebasedonastatelessrequest-responseframework.Inthesesortofapplications,itisuptothedevelopertoensuretherightcodewasputinplacetoensurethestateofwebsessionwasmaintainedwhiletheuserwasworkingwiththesystem.

ButwithNode.jswebapplications,youcannowworkinreal-timeandhavea2-waycommunication.Thestateismaintained,andtheeithertheclientorservercanstartthecommunication.

FeaturesofNode.jsLet'slookatsomeofthekeyfeaturesofNode.js

1. AsynchronouseventdrivenIOhelpsconcurrentrequesthandling–ThisisprobablythebiggestsellingpointsofNode.js.ThisfeaturebasicallymeansthatifarequestisreceivedbyNodeforsomeInput/Outputoperation,itwillexecutetheoperationinthebackgroundandcontinuewithprocessingotherrequests.

Thisisquitedifferentfromotherprogramminglanguages.Asimpleexampleofthisisgiveninthecodebelow

varfs=require('fs');

fs.readFile("Sample.txt",function(error,data)

{

console.log("ReadingDatacompleted");

});

TheabovecodesnippetlooksatreadingafilecalledSample.txt.Inotherprogramminglanguages,thenextlineofprocessingwouldonlyhappenoncetheentirefileisread.ButinthecaseofNode.jstheimportantfractionofcodetonoticeisthedeclarationofthefunction('function(error,data)').Thisisknownasacallbackfunction.Sowhathappenshereisthatthefilereadingoperationwillstartinthebackground.Andotherprocessingcanhappensimultaneouslywhilethefileisbeingread.Oncethefilereadoperationiscompleted,thisanonymousfunctionwillbecalledandthetext"ReadingDatacompleted"willbewrittentotheconsolelog.

2. NodeusestheV8JavaScriptRuntimeengine,theonewhichisusedbyGoogleChrome.NodehasawrapperovertheJavaScriptenginewhichmakestheruntimeenginemuchfasterandhenceprocessingofrequestswithinNodealsobecomefaster.

3. Handlingofconcurrentrequests–AnotherkeyfunctionalityofNodeistheabilitytohandleconcurrentconnectionswithaveryminimaloverheadonasingleprocess.

4. TheNode.jslibraryusedJavaScript–ThisisanotherimportantaspectofdevelopmentinNode.js.Amajorpartofthedevelopmentcommunityarealreadywellversedinjavascript,andhence,developmentinNode.jsbecomeseasierforadeveloperwhoknowsjavascript.

5. ThereareanActiveandvibrantcommunityfortheNode.jsframework.Becauseoftheactivecommunity,therearealwayskeysupdatesmadeavailabletotheframework.Thishelpstokeeptheframeworkalwaysup-to-datewiththelatesttrendsinwebdevelopment.

WhousesNode.js

Node.jsisusedbyavarietyoflargecompanies.Belowisalistofafewofthem.

Paypal–AlotofsiteswithinPaypalhavealsostartedthetransitionontoNode.js.LinkedIn-LinkedInisusingNode.jstopowertheirMobileServers,whichpowerstheiPhone,Android,andMobileWebproducts.MozillahasimplementedNode.jstosupportbrowserAPIswhichhashalfabillioninstalls.EbayhoststheirHTTPAPIserviceinNode.js

WhentouseandnotuseNode.jsNode.jsisbestforusageinstreamingorevent-basedreal-timeapplicationslike

1. Chatapplications2. Gameservers–Fastandhigh-performanceserversthatneedtoprocessesthousandsof

requestsatatime,thenthisisanidealframework.3. Goodforcollaborativeenvironment–Thisisgoodforenvironmentswhichmanage

document.Indocumentmanagementenvironmentyouwillhavemultiplepeoplewhoposttheirdocumentsanddoconstantchangesbycheckingoutandcheckingindocuments.SoNode.jsisgoodfortheseenvironmentsbecausetheeventloopinNode.jscanbetriggeredwheneverdocumentsarechangedinadocumentmanagedenvironment.

4. Advertisementservers–AgainhereyoucouldhavethousandsofrequesttopulladvertisementsfromthecentralserverandNode.jscanbeanidealframeworktohandlethis.

5. Streamingservers–AnotheridealscenariotouseNodeisformultimediastreamingserverswhereinclientshaverequest'stopulldifferentmultimediacontentsfromthisserver.

Node.jsisgoodwhenyouneedhighlevelsofconcurrencybutlessamountofdedicatedCPUtime.

Bestofall,sinceNode.jsisbuiltonjavascript,it'sbestsuitedwhenyoubuildclient-sideapplicationswhicharebasedonthesamejavascriptframework.

WhentonotuseNode.js

Node.jscanbeusedforalotofapplicationswithvariouspurpose,theonlyscenariowhereitshouldnotbeusedisiftherearelongprocessingtimeswhichisrequiredbytheapplication.

Nodeisstructuredtobesinglethreaded.Ifanyapplicationisrequiredtocarryoutsomelongrunningcalculationsinthebackground.Soiftheserverisdoingsomecalculation,itwon'tbeabletoprocessanyotherrequests.Asdiscussedabove,Node.jsisbestwhenprocessingneedslessdedicatedCPUtime.

Chapter2:Download&InstallNode.js

TostartbuildingyourNode.jsapplications,thefirststepistheinstallationofthenode.jsframework.TheNode.jsframeworkisavailableforavarietyofoperatingsystemsrightfromWindowstoUbuntuandOSX.OncetheNode.jsframeworkisinstalledyoucanstartbuildingyourfirstNode.jsapplications.

Node.jsalsohastheabilitytoembeddedexternalfunctionalityorextendedfunctionalitybymakinguseofcustommodules.Thesemoduleshavetobeinstalledseparately.AnexampleofamoduleistheMongoDBmodulewhichallowsyoutoworkwithMongoDBdatabasesfromyourNode.jsapplication.

Howtoinstallnode.jsThefirststepsinusingNode.jsistheinstallationoftheNode.jslibrariesontheclientsystem.ToperformtheinstallationofNode.js,performthebelowsteps;

Step1)Gotothesitehttps://nodejs.org/en/download/anddownloadthenecessarybinaryfiles.Inourexample,wearegoingtothedownloadthe32-bitsetupfilesforNode.js.

Step2)Doubleclickonthedownloaded.msifiletostarttheinstallation.ClicktheRunbuttoninthefirstscreentobegintheinstallation.

Step3)Inthenextscreen,clickthe"Next"buttontocontinuewiththeinstallation

Step4)InthenextscreenAcceptthelicenseagreementandclickontheNextbutton.

Step5)Inthenextscreen,choosethelocationwhereNode.jsneedstobeinstalledandthenclickontheNextbutton.

1. FirstenterthefilelocationfortheinstallationofNode.js.ThisiswherethefilesforNode.jswillbestoredaftertheinstallation.

2. ClickontheNextbuttontoproceedaheadwiththeinstallation.

Step6)Acceptthedefaultcomponentsandclickonthenextbutton.

Step7)Inthenextscreen,clicktheInstallbuttontostarttheinstallation.

Step8)ClicktheFinishbuttontocompletetheinstallation.

InstallingnodethroughapackagemanagerTheotherwaytoinstallNode.jsonanyclientmachineistousea"packagemanager".

Onwindows,thenodepackagemanagerisknownasChocolatey.Itwasdesignedtobeadecentralizedframeworkforquicklyinstallingapplicationsandtoolsthatyouneed.

ToinstallNode.jsviaChocolatey,thefollowingstepsneedtobeperformed.

Step1)InstallingChocolatey–TheChocolateywebsite(https://chocolatey.org/)hasveryclearinstructionsonhowthisframeworkneedstobeinstalled.

Thefirststepsistorunthebelowcommandinthecommandpromptwindows.ThiscommandistakenfromtheChocolateywebsiteandisthestandardcommandforinstallingNode.jsviaChocolatey.ThebelowcommandisaPowerShellcommandwhichcallstheremotePowerShellscriptontheChocolateywebsite.ThiscommandneedstoberuninaPowerShellcommandwindow.ThisPowerShellscriptdoesallthenecessaryworkofdownloadingtherequiredcomponentsandinstallingthemaccordingly.

@powershell-NoProfile-ExecutionPolicyBypass-Command"iex((new-objectwet.webclient).DownloadString('https://chocolatey.org/install.ps1'))"&&SETPATH=%PATH%;%ALLUSERSPROFILE%\chocolatey\bin

Step2)ThenextstepistoinstallNode.jstoyourlocalmachineusingtheChocolatey,packagemanager.Thiscanbedonebyrunningthebelowcommandinthecommandprompt.

cinstnodejsinstall

Iftheinstallationissuccessful,youwillgetthemessageofthesuccessfulinstallationofNode.js.

Note:Ifyougetanerrorlike“C:\ProgramData\chocolatey\lib\libreoffice\tools\chocolateyInstall.ps1”Thenmanuallycleatethefolderinthepath

RunningyourfirstHelloworldapplicationinNode.jsOnceyouhavedownloadedandinstalledNode.jsonyourcomputer,letstrytodisplay"HelloWorld"inawebbrowser.

CreatefileNode.jswithfilenamefirstprogram.js

varhttp=require('http');

http.createServer(function(req,res){

res.writeHead(200,{'Content-Type':'text/html'});

res.end('HelloWorld!');

}).listen(8080);

CodeExplanation:

1.Thebasicfunctionalityofthe"require"functionisthatitreadsaJavaScriptfile,executesthefile,andthenproceedstoreturnanobject.Usingthisobject,onecanthenusethevariousfunctionalitiesavailableinthemodulecalledbytherequirefunction.Soinourcase,sincewewanttousethefunctionalityofhttpandweareusingtherequire(http)command.

2.Inthis2ndlineofcode,wearecreatingaserverapplicationwhichisbasedonasimplefunction.Thisfunctioniscalled,wheneverarequestismadetoourserverapplication.

3.Whenarequestisreceived,weareaskingourfunctiontoreturna"HelloWorld"responsetotheclient.ThewriteHeadfunctionisusedtosendheaderdatatotheclientandwhiletheendfunctionwillclosetheconnectiontotheclient.

4.Wearethenusingthe.listenfunctiontomakeourserverapplicationlistentoclientrequestsonportno8080.Youcanspecifyanyavailableportoverhere.

ExecutingthecodeStep1)Savethefileonyourcomputer:C:\Users\YourName\firstprogram.js

Step2)Inthecommandprompt,navigatetothefolderwherethefikeisstored.Enterthecommand

Nodefirstprogram.js

Step3)Now,yourcomputerworksasaserver!Ifanyonetriestoaccessyourcomputeronport8080,theywillgeta"HelloWorld!"messageinreturn!

Step4)Startyourinternetbrowser,andtypeintheaddress:http://localhost:8080

OutPut

Summary

WehaveseentheinstallationofNode.jsviathemsiinstallationmodulewhichisavailableontheNode.jswebsite.ThisinstallationinstallsthenecessarymoduleswhicharerequiredtorunaNode.jsapplicationontheclient.Node.jscanalsobeinstalledviaapackagemanager.ThepackagemanagerforwindowsisknownasChocolatey.Byrunningsomesimplecommandsinthecommandprompt,theChocolateypackagemanagerautomaticallydownloadsthenecessaryfilesandtheninstallsthemontheclientmachine.AsimpleNode.jsapplicationconsistsofcreatingaserverwhichlistensonaparticularport.Whenarequestcomestotheserver,theclientautomaticallysendsa'HelloWorld'responsetotheclient.

Chapter3:Modules

AmoduleinNode.jsisalogicalencapsulationofcodeinasingleunit.It'salwaysagoodprogrammingpracticetoalwayssegregatecodeinsuchawaythatmakesitmoremanageableandmaintainableforfuturepurposes.That'swheremodulesinNode.jscomesinaction.

Sinceeachmoduleisanindependententitywithitsownencapsulatedfunctionality,itcanbemanagedasaseparateunitofwork.

Duringthistutorial,wewillseehowwecanmakeuseofmodulesinNode.js.

WhataremodulesinNode.js?Asstatedearlier,modulesinNodejsareawayofencapsulatingcodeinaseparatelogicalunit.TherearemanyreadymademodulesavailableinthemarketwhichcanbeusedwithinNodejs.

BelowaresomeofthepopularmoduleswhichareusedinaNodejsapplication

1. Expressframework–ExpressisaminimalandflexibleNodejswebapplicationframeworkthatprovidesarobustsetoffeaturesforthewebandmobileapplications.

2. Socket.io-Socket.IOenablesreal-timebidirectionalevent-basedcommunication.Thismoduleisgoodforcreationofchattingbasedapplications.

3. Jade-Jadeisahigh-performancetemplateengineandimplementedwithJavaScriptfornodeandbrowsers.

4.MongoDB-TheMongoDBNode.jsdriveristheofficiallysupportednode.jsdriverforMongoDB.

5. Restify-restifyisalightweightframework,similartoexpressforbuildingRESTAPIs6. Bluebird-Bluebirdisafullyfeaturedpromiselibrarywithfocusoninnovativefeatures

andperformance

UsingmodulesinNode.jsInordertousemodulesinaNode.jsapplication,theyfirstneedtobeinstalledusingtheNodepackagemanager.

Thebelowcommandlineshowshowamodule"express"canbeinstalled.

npminstallexpress

Theabovecommandwilldownloadthenecessaryfileswhichcontainthe"expressmodules"andtakecareoftheinstallationaswellOncethemodulehasbeeninstalled,inordertouseamoduleinaNode.jsapplicationyouneedtousethe'require'keyword.ThiskeywordisawaythatNode.jsusestoincorporatethefunctionalityofamoduleinanapplication.

Let'slookatanexamplehowwecanusethe"require"keyword.Thebelow"Guru99"codeexampleshowshowtousetherequirefunction

varexpress=require('express');

varapp=express();

app.set('viewemngine','jade');

app.get('/',function(req,res)

{

});

varserver=app.listen(3000,function()

{

});

1. Inthefirststatementitself,weareusingthe"require"keywordtoincludetheexpressmodule.The"express"moduleisanoptimizedJavaScriptlibraryforNode.js

development.ThisisoneofthemostcommonlyusedNode.jsmodules.2. Afterthemoduleisincluded,inordertousethefunctionalitywithinthemodule,anobject

needstobecreated.Hereanobjectoftheexpressmoduleiscreated.3. Oncethemoduleisincludedusingthe"require"commandandan"object"iscreated,the

requiredmethodsoftheexpressmodulecanbeinvoked.Hereweareusingthesetcommandtosettheviewengine,whichisusedtosetthetemplatingengineusedinNode.js.Note:-(Justforthereader'sunderstanding,atemplatingengineisanapproachforinjectingvaluesinanapplicationbypickingupdatafromdatafiles.ThisconceptisprettyfamousinAngularJSwhereinthecurlybraces{{key}}isusedtosubstitutesvaluesinthewebpage.Theword'key'inthecurlybracesbasicallydenotesthevariablewhichwillbesubstitutedbyavaluewhenthepageisdisplayed.)

4. Hereweareusingthelistenmethodtomaketheapplicationlistenonaparticularportnumber.

CreatingNPMmodulesNode.jshastheabilitytocreatecustommodulesandallowsyoutoincludethosecustommodulesinyourNode.jsapplication.

Let'slookatasimpleexampleofhowwecancreateourownmoduleandincludethatmoduleinourmainapplicationfile.Ourmodulewilljustdoasimpletaskofadding2numbers.

Let'sfollowthebelowstepstoseehowwecancreatemodulesandincludetheminourapplication.

Step1)Createafilecalled"Addition.js"andincludethebelowcode.Thisfilewillcontainthelogicforyourmodule.

Belowisthecodewhichwouldgointothisfile;

varexports=module.exports={};

exports.AddNumber=function(a,b)

{

returna+b;

};

1. The"exports"keywordisusedtoensurethatthefunctionalitydefinedinthisfilecanactuallybeaccessedbyotherfiles.

2. Wearethendefiningafunctioncalled'AddNumber'.Thisfunctionisdefinedtotake2parameters,aandb.Thefunctionisaddedtothemodule"exports"tomakethefunctionasapublicfunctionthatcanbeaccessedbyotherapplicationmodules.

3. Wearefinallymakingourfunctionreturntheaddedvalueoftheparameters.

Nowthatwehavecreatedourcustommodulewhichhasthefunctionalityofadding2numbers.It'snowtimetocreateanapplication,whichwillcallthismodule.

Inthenextstep,wewillactuallyseehowtocreatetheapplicationwhichwillcallourcustommodule.

Step2)Createafilecalled"app.js,"whichisyourmainapplicationfileandaddthebelowcode

varAddition=require('./Addition.js');

console.log(Addition.AddNumber(1,2));

1. Weareusingthe"require"keywordtoincludethefunctionalityintheAddition.jsfile.2. SincethefunctionsintheAddition.jsfilearenowaccessible,wecannowmakeacallto

theAddNumberfunction.Inthefunction,wearepassing2numbersasparameters.Wearethendisplayingthevalueintheconsole.

Output:

Whenyouruntheapp.jsfile,youwillgetanoutputofvalue3intheconsolelog.TheresultisbecausetheAddNumberfunctionintheAddition.jsfilewascalledsuccessfullyandthereturnedvalueof3wasdisplayedintheconsole.

Note:-Wearenotusingthe"Nodepackagemanager"asofyettoinstallourAddition.jsmodule.Thisisbecausethemoduleisalreadypartofourprojectonthelocalmachine.TheNodepackagemanagercomesinthepicturewhenyoupublishamoduleontheinternetwhichweseeinthesubsequenttopic.

ExtendingmodulesWhencreatingmodules,itisalsopossibletoextendorinheritonemodulefromanother.

Inmoderndayprogramming,it'squitecommontobuildalibraryofcommonmodulesandthenextendthefunctionalityofthesecommonmodulesifrequired.

Let'slookatanexampleofhowwecanextendmodulesinNode.js.

Step1)Createthebasemodule.

Inourexample,createafilecalled"Tutorial.js"andplacethebelowcode.

Inthiscode,wearejustcreatingafunctionwhichreturnsastringtotheconsole.Thestringreturnedis"Guru99Tutorial".


exports.tutorial=function()

{

console.log("Guru99Tutotial")

}

1. TheexportsmoduleisusedsothatwhateverfunctionisdefinedinthisfilecanbeavailableinothermodulesinNode.js

2. WearecreatingafunctioncalledtutorialwhichcanbeusedinotherNode.jsmodules.3. Wearedisplayingastring"Guru99Tutorial"intheconsolewhenthisfunctioniscalled.

NowthatwehavecreatedourbasemodulecalledTutorial.js.It'snowtimetocreateanothermodulewhichwillextendthisbasemodule.

Wewillexplorehowtodothisinthenextstep.

Step2)Nextwewillcreateourextendedmodule.Createanewfilecalled"NodeTutorial.js"andplacethebelowcodeinthefile.

varTutor=require('./Tutorial.js');

exports.NodeTutorial=function()

{

console.log("NodeTutorial")

functionpTutor()

{

varPTutor=Tutor

PTutor.tutorial;

}

}

Note,thefollowingkeypointsabouttheabovecode

1. Weareusingthe"require"functioninthenewmodulefileitself.Sincewearegoingtoextendtheexistingmodulefile"Tutorial.js",weneedtofirstincludeitbeforeextendingit.

2. Wethencreateafunctioncalled"Nodetutorial."Thisfunctionwilldo2things,

Itwillsendastring"NodeTutorial"totheconsole.Itwillsendthestring"Guru99Tutorial"fromthebasemodule"Tutorial.js"toourextendedmodule"NodeTutorial.js".

1. Herewearecarryingoutthefirststeptosendastringto"NodeTutorial"totheconsole.2. ThenextstepistocallthefunctionfromourTutorialmodule,whichwilloutputthestring

"Guru99Tutorial"totheconsole.log.

Step3)Createyourmainapp.jsfilewhichisyourmainapplicationfileandincludethebelowcode.

varlocalTutor=require('./NodeTutorial.js');

localTutor.NodeTutorial();

localTutor.NodeTutorial.pTutor();

Theabovecodedoesthefollowingthings;

1. Ourmainapplicationfilenowcallsthe"NodeTutorial"module.2. Wearecallingthe"NodeTutorial"function.Bycallingthisfunction,thetext"Node

Tutorial"willbedisplayedintheconsolelog.3. SincewehaveextendedourTutorial.jsmoduleandexposedafunctioncalledpTutor.It

alsocallsthetutorialmoduleintheTutorial.jsmodule,andthetext"Guru99Tutorial"willbedisplayedtotheconsoleaswell.

Output:

Sincewehaveexecutedtheaboveapp.jscodeusingNode,wewillgetthefollowingoutputintheconsole.logfile

NodeTutorialGuru99Tutorial

PublishingNPM(NodePackageManager)ModulesOnecanpublishtheirownmoduletotheirownGithubrepository.

Bypublishingyourmoduletoacentrallocation,youarethennotburdenedwithhavingtoinstallyourselfoneverymachinethatrequiresit.

Instead,youcanusetheinstallcommandofnpmandinstallyourpublishednpmmodule.

Thefollowingstepsneedtobefollowedtopublishyournpmmodule

Step1)CreateyourrepositoryonGitHub(anonlinecoderepositorymanagementtool).Itcanbeusedforhostingyourcoderepositories.

Step2)Youneedtotellyourlocalnpminstallationonwhoyouare.Whichmeansthatweneedtotellnpmwhoistheauthorofthismodule,whatistheemailidandanycompanyURL,whichisavailablewhichneedstobeassociatedwiththisid.Allofthesedetailswillbeaddedtoyournpmmodulewhenitispublished.

Thebelowcommandssetsthename,emailandURLoftheauthorofthenpmmodule.

npmsetinit.author.name"Guru99."

npmsetinit.author.email"[email protected]"

npmsetinit.author.urlhttp://Guru99.com

Step3)Thenextstepistologinintonpmusingthecredentialsprovidedinthelaststep.Tologin,youneedtousethebelowcommand

npmlogin

Step4)Initializeyourpackage–Thenextstepistoinitializethepackagetocreatethepackage.jsonfile.Thiscanbedonebyissuingthebelowcommand

npminit

Whenyouissuetheabovecommand,youwillbepromptedforsomequestions.Themostimportantoneistheversionnumberforyourmodule.

Step5)PublishtoGitHub–ThenextstepistopublishyoursourcefilestoGitHub.Thiscanbedonebyrunningthebelowcommands.

gitadd.

gitcommit-m"Initialrelease"

gittagv0.0.1

gitpushoriginmaster--tags

Step6)Publishyourmodule–Thefinalbitistopublishyourmoduleintothenpmregistry.Thisisdoneviathebelowcommand.

npmpublish

ManagingthirdpartypackageswithnpmAswehaveseen,the"Nodepackagemanager"hastheabilitytomanagemodules,whicharerequiredbyNode.jsapplications.

Let'slookatsomeofthefunctionsavailableinthenodepackagemanagerformanagingmodules

1. Installingpackagesinglobalmode–Modulescanbeinstalledatthegloballevel,whichjustbasicallymeansthatthesemoduleswouldbeavailableforallNode.jsprojectsonalocalmachine.Theexamplebelowshowshowtoinstallthe"expressmodule"withtheglobaloption.

npminstallexpress–global

Theglobaloptionintheabovestatementiswhatallowsthemodulestobeinstalledatagloballevel.

2. Listingalloftheglobalpackagesinstalledonalocalmachine.Thiscanbedonebyexecutingthebelowcommandinthecommandpromptnpmlist--global

Belowistheoutputwhichwillbeshown,ifyouhavepreviouslyinstalledthe"expressmodule"onyoursystem.

Hereyoucanseethedifferentmodulesinstalledonthelocalmachine.

3. Installingaspecificversionofapackage–Sometimestheremaybearequirementtoinstalljustthespecificversionofapackage.Onceyouknowwhatisthepackageandtherelevantversionthatneedstobeinstalled,youcanusethenpminstallcommandtoinstallthatspecificversion.Theexamplebelowshowshowtoinstallthemodulecalledunderscorewithaspecificversionof1.7.0

[email protected]

4. Updatingapackageversion–Sometimesyoumayhaveanolderversionofapackageinasystem,andyoumaywanttoupdatetothelatestoneavailableinthemarket.Todothisonecanusethenpmupdatecommand.Theexamplebelowshowshowtoupdatetheunderscorepackagetothelatestversion

npmupdateunderscore

5. Searchingforaparticularpackage–Tosearchwhetheraparticularversionisavailableonthelocalsystemornot,youcanusethesearchcommandofnpm.Theexamplebelowwillcheckiftheexpressmoduleisinstalledonthelocalmachineornot.npmsearchexpress

6. Un-installingapackage–Thesameinwhichyoucaninstallapackage,youcanalsoun-installapackage.Theuninstallationofapackageisdonewiththeuninstallationcommandofnpm.Theexamplebelowshowshowtouninstalltheexpressmodule

npmuninstallexpress

Whatisthepackage.jsonfileThe"package.json"fileisusedtoholdthemetadataaboutaparticularproject.ThisinformationprovidestheNodepackagemanagerthenecessaryinformationtounderstandhowtheprojectshouldbehandledalongwithitsdependencies.

Thepackage.jsonfilescontainsinformationsuchastheprojectdescription,theversionoftheprojectinaparticulardistribution,licenseinformation,andconfigurationdata.

Thepackage.jsonfileisnormallylocatedattherootdirectoryofaNode.jsproject.

Let'stakeanexampleofhowthestructureofamodulelookswhenitisinstalledvianpm.

ThebelowsnapshotshowsthefilecontentsoftheexpressmodulewhenitisincludedinyourNode.jsproject.Fromthesnapshot,youcanseethepackage.jsonfileintheexpressfolder.

Ifyouopenthepackage.jsonfileyouwillseealotofinformationinthefile.

Belowisasnapshotofaportionofthefile.Theexpress@~4.13.1mentionstheversionnumberoftheexpressmodulebeingused.

Summary

AmoduleinNode.jsisalogicalencapsulationofcodeinasingleunit.SeparationintomodulesmakescodemoremanageableandmaintainableforfuturepurposesTherearemanymodulesavailableinthemarketwhichcanbeusedwithinNode.jssuchasexpress,underscore,mongoDB,etc.Thenodepackagemanager(npm)isusedtodownloadandinstallmoduleswhichcanthenbeusedinaNode.jsapplication.OnecancreatecustomNPMmodules,extendthesemodulesandalsopublishthesemodules.TheNodepackagemanagerhasacompletesetofcommandstomanagethenpmmodulesonthelocalsystemsuchastheinstallation,un-installation,searching,etc.Thepackage.jsonfileisusedtoholdtheentiremetadatainformationforannpmmodule.

Chapter4:CreateServerandGetData

TheNode.jsframeworkismostlyusedtocreateserverbasedapplications.Theframeworkcaneasilybeusedtocreatewebserverswhichcanservecontenttousers.

Thereareavarietyofmodulessuchasthe"http"and"request"module,whichhelpsinprocessingserverrelatedrequestsinthewebserverspace.WewillhavealookathowwecancreateabasicwebserverapplicationusingNodejs.

NodeaswebserverusingHTTPLet'slookatanexampleofhowtocreateandrunourfirstNodejsapplication.

Ourapplicationisgoingtocreateasimpleservermodulewhichwilllistenonportno7000.Ifarequestismadethroughthebrowseronthisportno,thenserverapplicationwillsenda'Hello'World'responsetotheclient.

varhttp=require('http')

varserver=http.createServer((function(request,response)

{

response.writeHead(200,

{"Content-Type":"text/plain"));

response.end("HelloWorld\n");

}));

server.listen(7000);

CodeExplanation:

1. Thebasicfunctionalityoftherequirefunctionisthatitreadsajavascriptfile,executesthefile,andthenproceedstoreturntheexportsobject.Soinourcase,sincewewanttousethefunctionalityofthehttpmodule,weusetherequirefunctiontogettherequiredfunctionsfromthehttpmodulesothatitcanbeusedinourapplication.

2. Inthislineofcode,wearecreatingaserverapplicationwhichisbasedonasimplefunction.Thisfunctioniscalledwheneverarequestismadetoourserverapplication.

3. Whenarequestisreceived,wearesayingtosendaresponsewithaheadertypeof'200.'Thisnumberisthenormalresponsewhichissentinanhttpheaderwhenasuccessfulresponseissenttotheclient.

4. Intheresponseitself,wearesendingthestring'HelloWorld.'5. Wearethenusingtheserver.listenfunctiontomakeourserverapplicationlistentoclient

requestsonportno7000.Youcanspecifyanyavailableportoverhere.

Ifthecommandisexecutedsuccessfully,thefollowingOutputwillbeshownwhenyourunyourcodeinthebrowser.

Output:

Fromtheoutput,

YoucanclearlyseethatifwebrowsetotheURLoflocalhostonport7000,youwillseethestring'HelloWorld'displayedinthepage.Becauseinourcodewehavementionedspecificallyfortheservertolistenonportno7000,weareabletoviewtheoutputwhenbrowsingtothisurl.

Hereisthecodeforyourreference

varhttp=require('http')

varserver=http.createServer((function(request,response)

{

response.writeHead(200,

{"Content-Type":"text/plain"));

response.end("HelloWorld\n");

}));

server.listen(7000);

HandlingGETRequestsinNode.jsMakingaGETRequesttogetthedatafromanothersiteisrelativelyverysimpleinNode.js.TomakeaGetrequestinthenode,weneedtofirsthavetherequestmoduleinstalled.Thiscanbedonebyexecutingthefollowinglineinthecommandline

npminstallrequest

TheabovecommandrequeststheNodepackagemanagertodownloadtherequiredrequestmodulesandinstallthemaccordingly.

Whenyournpmmodulehasbeeninstalledsuccessfully,thecommandlinewillshowtheinstalledmodulenameandversion:<name>@<version>.

Intheabovesnapshot,youcanseethatthe'request'modulealongwiththeversionnumber2.67.0wasdownloadedandinstalled.

Nowlet'sseethecodewhichcanmakeuseofthis'request'command.

varrequest=require("request");

request("http://www.google.com",function(error,response,body)

{

console.log(body);

});

CodeExplanation:

1. Weareusingthe'require'modulewhichwasinstalledinthelaststep.ThismodulehasthenecessaryfunctionswhichcanbeusedtomakeGETrequeststowebsites.

2. WearemakingaGETRequesttowww.google.comandsubsequentlycallingafunctionwhenaresponseisreceived.Whenaresponseisreceivedtheparameters(error,response,andbody)willhavethefollowingvaluesa. Error–IncasethereisanyerrorreceivedwhenusingtheGETrequest,thiswillbe

recordedhere.b. Response-Theresponsewillhavethehttpheaderswhicharesentbackinthe

response.c. Body-ThebodywillcontaintheentirecontentoftheresponsesentbyGoogle.

3. Inthis,wearejustwritingthecontentreceivedinthebodyparametertotheconsole.logfile.Sobasically,whateverwegetbygoingtowww.google.comwillbewrittentotheconsole.log.


varrequest=require("request");

request("http://www.google.com",function(error,response,body)

{

console.log(body);

});

Summary

TheNode.jsframeworkcanbeusedtodevelopwebserversusingthe'http'module.Theapplicationcanbemadetolistenonaparticularportandsendaresponsetotheclientwheneverarequestismadetotheapplication.The'request'modulecanbeusedtogetinformationfromwebsites.Theinformationwouldcontaintheentirecontentofthewebpagerequestedfromtherelevantwebsite.

Chapter5:Node.jswithExpress

Inthistutorial,wewillalsohavealookattheexpressframework.ThisframeworkisbuiltinsuchawaythatitactsasaminimalandflexibleNode.jswebapplicationframework,providingarobustsetoffeaturesforbuildingsingleandmultipage,andhybridwebapplication.

WhatisExpress.jsExpress.jsisaNodejswebapplicationserverframework,whichisspecificallydesignedforbuildingsingle-page,multi-page,andhybridwebapplications.

Ithasbecomethestandardserverframeworkfornode.js.ExpressisthebackendpartofsomethingknownastheMEANstack.

TheMEANisafreeandopen-sourceJavaScriptsoftwarestackforbuildingdynamicwebsitesandwebapplicationswhichhasthefollowingcomponents;

1)MongoDB-ThestandardNoSQLdatabase

2)Express.js-Thedefaultwebapplicationsframework

3)Angular.js-TheJavaScriptMVCframeworkusedforwebapplications

4)Node.js-Frameworkusedforscalableserver-sideandnetworkingapplications.

TheExpress.jsframeworkmakesitveryeasytodevelopanapplicationwhichcanbeusedtohandlemultipletypesofrequestsliketheGET,PUT,andPOSTandDELETErequests.

InstallingandusingExpressExpressgetsinstalledviatheNodePackagemanager.Thiscanbedonebyexecutingthefollowinglineinthecommandline

npminstallexpress

TheabovecommandrequeststheNodepackagemanagertodownloadtherequiredexpressmodulesandinstallthemaccordingly.

Let'suseournewlyinstalledExpressframeworkandcreateasimple"HelloWorld"application.

Ourapplicationisgoingtocreateasimpleservermodulewhichwilllistenonportno3000.Inourexample,ifarequestismadethroughthebrowseronthisportno,thenserverapplicationwillsenda'Hello'World'responsetotheclient.


varapp=express();


{

res.send('HelloWorld!');

});

varserver=app.listen(3000,function(){});

CodeExplanation:

1. Inourfirstlineofcode,weareusingtherequirefunctiontoincludethe"expressmodule."2. Beforewecanstartusingtheexpressmodule,weneedtomakeanobjectoftheexpress

module.3. Herewearecreatingacallbackfunction.Thisfunctionwillbecalledwheneveranybody

browsestotherootofourwebapplicationwhichishttp://localhost:3000.Thecallbackfunctionwillbeusedtosendthestring'HelloWorld'tothewebpage.

4. Inthecallbackfunction,wearesendingthestring"HelloWorld"backtotheclient.The'res'parameterisusedtosendcontentbacktothewebpage.This'res'parameterissomethingthatisprovidedbythe'request'moduletoenableonetosendcontentbacktothewebpage.

5. Wearethenusingthelistentofunctiontomakeourserverapplicationlistentoclientrequestsonportno3000.Youcanspecifyanyavailableportoverhere.3


Output:

Fromtheoutput,

YoucanclearlyseethatweifbrowsetotheURLoflocalhostonport3000,youwillseethestring'HelloWorld'displayedinthepage.Becauseinourcodewehavementionedspecificallyfortheservertolistenonportno3000,weareabletoviewtheoutputwhenbrowsingtothisURL.

WhatareRoutesRoutingrefersfordeterminingthewayinwhichanapplicationrespondstoaclientrequesttoaparticularendpoint.

Forexample,aclientcanmakeaGET,POST,PUTorDELETEhttprequestforvariousURL'ssuchastheone'sshownbelow;

http://localhost:3000/Books

http://localhost:3000/Students

Intheaboveexample,

IfaGETrequestismadeforthefirstURL,thentheresponseshouldideallybealistofbooks.IftheGETrequestismadeforthesecondURL,thentheresponseshouldideallybealistofStudents.SobasedontheURLwhichisaccessed,adifferentfunctionalityonthewebserverwillbeinvokedandaccordinglytheresponsewillbesenttotheclient.Thisistheconceptofrouting.

Eachroutecanhaveoneormorehandlerfunctions,whichareexecutedwhentherouteismatched.

Thegeneralsyntaxforarouteisshownbelow

app.METHOD(PATH,HANDLER)

Wherein,

1)appisaninstanceoftheexpressmodule

2)METHODisanHTTPrequestmethod(GET,POST,PUTorDELETE)

3)PATHisapathontheserver.

4)HANDLERisthefunctionexecutedwhentherouteismatched.

Let'slookatanexampleofhowwecanimplementroutesinexpress.Ourexamplewillcreate3routesas

1. A/Noderoutewhichwilldisplaythestring"TutorialonNode"ifthisrouteisaccessed2. A/Angularroutewhichwilldisplaythestring"TutorialonAngular"ifthisrouteis

accessed3. Adefaultroute/whichwilldisplaythestring"WelcometoGuru99Tutorials."

Ourbasiccodewillremainthesameaspreviousexamples.Thebelowsnippetisanadd-ontoshowcasehowroutingisimplemented.

app.route('/Node).get(function(req.res)

{

res.send("TutorialonNode");

});

app.route('/Angular).get(function(req.res)

{

res.send("TutorialonAngular");

});


{

res.send('WelcometoGuru99Tutorials');

});

CodeExplanation:

1. HerewearedefiningarouteiftheURLhttp://localhost:3000/Nodeisselectedinthebrowser.Totheroute,weareattachingacallbackfunctionwhichwillbecalledwhenwebrowsetotheNodeURL.

Thefunctionhas2parameters.

Themainparameterwewillbeusingisthe'res'parameterwhichcanbeusedtosendinformationbacktotheclient.The'req'parameterhasinformationabouttherequestbeingmade.Sometimesadditionalparameterscouldbesentaspartoftherequestbeingmade,andhencethe'req'parametercanbeusedtofindtheadditionalparametersbeingsent.

2. Weareusingthesendfunctiontosendthestring"TutorialonNode"backtotheclientiftheNoderouteischosen.

3. HerewearedefiningarouteiftheURLhttp://localhost:3000/Angularisselectedinthebrowser.Totheroute,weareattachingacallbackfunctionwhichwillbecalledwhenwebrowsetotheAngularURL.

4. Weareusingthesendfunctiontosendthestring"TutorialonAngular"backtotheclientiftheAngularrouteischosen.

5. Thisisthedefaultroutewhichischosenwhenonebrowsestotherouteoftheapplication–http://localhost:3000.Whenthedefaultrouteischosen,themessage"WelcometoGuru99Tutorials"willbesenttotheclient.


Output:

Fromtheoutput,

YoucanclearlyseethatweifbrowsetotheURLoflocalhostonport3000,youwillseethestring'WelcometoGuru99Tutorials'displayedonthepage.Becauseinourcode,wehavementionedthatourdefaultURLwoulddisplaythismessage.

Fromtheoutput,

YoucanseethatiftheURLhasbeenchangedto/Node,therespectiveNoderoutewouldbechosenandthestring"TutorialOnNode'isdisplayed.

Fromtheoutput,

YoucanseethatiftheURLhasbeenchangedto/Angular,therespectiveNoderoutewouldbechosenandthestring"TutorialOnAngular"isdisplayed.

SampleWebserverusingexpress.jsFromouraboveexample,wehaveseenhowwecandecideonwhatoutputtoshowbasedonrouting.Thissortofroutingiswhatisusedinmostmoderndaywebapplications.TheotherpartofawebserverisaboutusingtemplatesinNodejs.

Whencreatingquickon-the-flyNodeapplications,aneasyandfastwayistousetemplatesfortheapplication.Therearemanyframeworksavailableinthemarketformakingtemplates.Inourcase,wewilltaketheexampleofthejadeframeworkfortemplating.

JadegetsinstalledviatheNodePackagemanager.Thiscanbedonebyexecutingthefollowinglineinthecommandline

npminstalljade

TheabovecommandrequeststheNodepackagemanagertodownloadtherequiredjademodulesandinstallthemaccordingly.

Let'suseournewlyinstalledjadeframeworkandcreatesomebasictemplates.

Step1)Thefirststepistocreateajadetemplate.Createafilecalledindex.jadeandinsertthebelowcode

1. Herewearespecifyingthatthetitleofthepagewillbechangedtowhatevervalueispassedwhenthistemplategetsinvoked.

2. Wearealsospecifyingthatthetextintheheadertagwillgetreplacedtowhatevergetspassedinthejadetemplate.


varapp=express();

app.set('viewengine','jade');


{

res.render('index',

{title:'Guru99',message:'Welcome'})

});


CodeExplanation:

1. Thefirstthingtospecifyintheapplicationis"viewengine"thatwillbeusedtorenderthetemplates.Sincewearegoingtousejadetorenderourtemplates,wespecifythisaccordingly.

2. Therenderfunctionisusedtorenderawebpage.Inourexample,wearerenderingthetemplate(index.jade)whichwascreatedearlier.

3. Wearepassingthevaluesof"Guru99"and"Welcome"totheparameters"title"and"message"respectively.Thesevalueswillbereplacedbythe'title',and'message'parametersdeclaredintheindex.jadetemplate.


Output:

Fromtheoutput,

Wecanseethatthetitleofthepagegetssetto"Guru99"andtheheaderofthepagegetssetto"Welcome."Thisisbecauseofthejadetemplatewhichgetsinvokedinournodejsapplication.

Summary

TheexpressframeworkisthemostcommonframeworkusedfordevelopingNodejsapplications.Theexpressframeworkisbuiltontopofthenode.jsframeworkandhelpsinfast-trackingdevelopmentofserverbasedapplications.Routesareusedtodivertuserstodifferentpartsofthewebapplicationsbasedontherequestmade.Theresponseforeachroutecanbevarieddependingonwhatneedstobeshowntotheuser.Templatescanbeusedtoinjectcontentinanefficientmanner.JadeisoneofthemostpopulartemplatingenginesusedinNode.jsapplications.

Chapter6:Node.jswithMongoDB

Mostlyallmoderndaywebapplicationshavesomesortofdatastoragesystematthebackendtostoredata.Forexample,ifyoutakethecaseofawebshoppingapplication,datasuchasthepriceofanitemorthenumberofitemsofaparticulartypewouldbestoredinthedatabase.

TheNodejsframeworkhastheabilitytoworkwithdatabaseswhicharecommonlyrequiredbymostmoderndaywebapplications.Nodejscanworkwithbothrelational(suchasOracleandMSSQLServer)andnon-relationaldatabases(suchasMongoDBandMySQL).Duringthistutorial,wewillseehowwecanusedatabasesfromwithinNodejsapplications.

Node.jsandNoSQLDatabasesOvertheyears,NoSQLdatabasesuchasMongoDBandMySQLhavebecomequitepopularasdatabasesforstoringdata.Theabilityofthesedatabasestostoreanysortofcontentandparticularlyinanysortofformatiswhatmakesthesedatabasessofamous.

Node.jshastheabilitytoworkwithbothMySQLandMongoDBasdatabases.Inordertouseeitherofthesedatabases,youneedtodownloadandusetherequiredmodulesusingtheNodepackagemanager.

ForMySQL,therequiredmoduleiscalled"mysql"andforusingMongoDBtherequiredmoduletobeinstalledis"Mongoose."

Withthesemodules,youcanperformthefollowingoperationsinNode.js

1. Managetheconnectionpooling–HereiswhereyoucanspecifythenumberofMySQLdatabaseconnectionsthatshouldbemaintainedandsavedbyNode.js.

2. Createandcloseaconnectiontoadatabase.Ineithercase,youcanprovideacallbackfunctionwhichcanbecalledwheneverthe"create"and"close"connectionmethodsareexecuted.

3. Queriescanbeexecutedtogetdatafromrespectivedatabasestoretrievedata.4. Datamanipulationsuchasinsertingdata,deletingandupdatingdatacanalsobeachieved

withthesemodules.

Fortheremainingtopics,wewilllookathowwecanworkwithMongoDBdatabaseswithinNode.js.

UsingMongoDBandNode.jsAsdiscussedintheearliertopic,MongoDBisoneofthemostpopulardatabasesusedalongwithNode.js.

Duringthischapter,wewillsee

HowwecanestablishconnectionswithaMongoDBdatabase

Howwecanperformthenormaloperationsofreadingdatafromadatabaseaswellasinserting,deletingandupdatingrecordsinamongoDBdatabase.

Forthepurposeofthischapter,let'sassumethatwehavethebelowmongoDBdatainplace.

Databasename:EmployeeDB

Collectionname:Employee

Documents

{

{Employeeid:1,EmployeeName:Guru99},

{Employeeid:2,EmployeeName:Joe},

{Employeeid:3,EmployeeName:Martin},

}

1. InstallingtheNPMModulesToaccessMongofromwithinaNodeapplication,adriverisrequired.TherearenumberofMongodriversavailable,butMongoDBisamongthemostpopular.ToinstalltheMongoDBmodule,runthebelowcommandnpminstallmongodb

2. CreatingandclosingaconnectiontoaMongoDBdatabase.ThebelowcodesnippetshowshowtocreateandcloseaconnectiontoaMongoDBdatabase.

varMongoClient=require('mongodb').MongoClient;

varurl='mongodb://localhost/EmployeeDB';

MongoClient.connect(url,function(err,db){

cursor.log("connected");

db.close();

});

CodeExplanation:

1. Thefirststepistoincludethemongoosemodulewhichisdonethroughtherequirefunction.Oncethismoduleisinplace,wecanusethenecessaryfunctionsavailableinthismoduletocreateconnectionstothedatabase.

2. Nextwespecifyourconnectstringtothedatabase.Intheconnectstringthereare3keyvalueswhicharepassed.

Thefirstis'mongodb'whichspecifiesthatweareconnectingtoamongoDBdatabase.Thenextis'localhost'whichmeansweareconnectingtoadatabaseonthelocalmachine.Thenextis'EmployeeDB'whichisthenameofthedatabasedefinedinourMongoDBdatabase.

3. Thenextstepistoactuallyconnecttoourdatabase.TheconnectfunctiontakesinourURLandhasthefacilitytospecifyacallbackfunction.Itwillbecalledwhentheconnectionisopenedtothedatabase.Thisgivesustheopportunitytoknowifthedatabaseconnectionwassuccessfulornot.

4. Inthefunction,wearewritingthestring"Connectionestablished"totheconsoletoindicatethatasuccessfulconnectionwascreated.

5. Finally,weareclosingtheconnectionusingthedb.closestatement.

Iftheabovecodeisexecutedproperly,thestring"Connected"willbewrittentotheconsoleasshownbelow.

3. QueryingfordatainaMongoDBdatabase–UsingtheMongoDBdriverwecanalsofetchdatafromtheMongoDBdatabase.

ThebelowsectionwillshowhowwecanusethedrivertofetchallofthedocumentsfromourEmployeecollection(ThisisthecollectioninourMongoDBdatabasewhichcontainsalltheemployeerelateddocuments.Eachdocumenthasanobjectid,Employeenameandemployeeidtodefinethevaluesofthedocument)inourEmployeeDBdatabase.




varcursor=db.collection('Employee').find();

cursor.each(function(err,doc){

console.log(doc);

});

});

CodeExplanation:

1. Inthefirststep,wearecreatingacursor(Acursorisapointerwhichisusedtopointtothevariousrecordsfetchedfromadatabase.Thecursoristhenusedtoiteratethroughthedifferentrecordsinthedatabase.Herewearedefiningavariablenamecalledcursorwhichwillbeusedtostorethepointertotherecordsfetchedfromthedatabase.)whichpointstotherecordswhicharefetchedfromtheMongoDbcollection.Wealsohavethefacilityofspecifyingthecollection'Employee'fromwhichtofetchtherecords.Thefind()functionisusedtospecifythatwewanttoretrieveallofthedocumentsfromtheMongoDBcollection.

2. Wearenowiteratingthroughourcursorandforeachdocumentinthecursorwearegoingtoexecuteafunction.

3. Ourfunctionissimplygoingtoprintthecontentsofeachdocumenttotheconsole.

Note:-Itisalsopossibletofetchaparticularrecordfromadatabase.Thiscanbedonebyspecifyingthesearchconditioninthefind()function.Forexample,supposeifyoujustwantedtofetchtherecordwhichhastheemployeenameasGuru99thenthisstatementcanbewrittenasfollows"varcursor=db.collection('Employee').find()."

Iftheabovecodeisexecutedsuccessfully,thefollowingoutputwillbedisplayedinyourconsole.

Output:

Fromtheoutput,

Youwillbeabletoclearlyseethatallthedocumentsfromthecollectionareretrieved.Thisispossiblebyusingthefind()methodofthemongoDBconnection(db)anditeratingthroughallofthedocumentsusingthecursor.

4. Insertingdocumentsinacollection–DocumentscanbeinsertedintoacollectionusingtheinsertOnemethodprovidedbytheMongoDBlibrary.ThebelowcodesnippetshowshowwecaninsertadocumentintoamongoDBcollection.




db.collection('Employee').insertOne({

Employeeid:4,

EmployeeName:"NewEmployee"

});

});

CodeExplanation:

1. HereweareusingtheinsertOnemethodfromtheMongoDBlibrarytoinsertadocumentintotheEmployeecollection.

2. WearespecifyingthedocumentdetailsofwhatneedstobeinsertedintotheEmployeecollection.

IfyounowcheckthecontentsofyourMongoDBdatabase,youwillfindtherecordwithEmployeeidof4andEmployeeNameof"NewEmployee"insertedintotheEmployeecollection.

Note:Theconsolewillnotshowanyoutputbecausetherecordisbeinginsertedinthedatabaseandnooutputcanbeshownhere.

Tocheckthatthedatahasbeenproperlyinsertedinthedatabase,youneedtoexecutethefollowingcommandsinMongoDB

1. UseEmployeeDB2. db.Employee.find({Employeeid:4})

ThefirststatementensuresthatyouareconnectedtotheEmployeeDbdatabase.Thesecondstatementsearchesfortherecordwhichhastheemployeeidof4.

5. Updatingdocumentsinacollection-DocumentscanbeupdatedinacollectionusingtheupdateOnemethodprovidedbytheMongoDBlibrary.ThebelowcodesnippetshowshowtoupdateadocumentinamongoDBcollection.




db.collection('Employee').updateOne({

"EmployeeName":"NewEmployee"

},{

$set:{

"EmployeeName":"Mohan"

}

});

});

CodeExplanation:

1. Hereweareusingthe"updateOne"methodfromtheMongoDBlibrary,whichisusedtoupdateadocumentinamongoDBcollection.

2. Wearespecifyingthesearchcriteriaofwhichdocumentneedstobeupdated.Inourcase,wewanttofindthedocumentwhichhastheEmployeeNameof"NewEmployee."

3. WethenwanttosetthevalueoftheEmployeeNameofthedocumentfrom"NewEmployee"to"Mohan".

IfyounowcheckthecontentsofyourMongoDBdatabase,youwillfindtherecordwithEmployeeidof4andEmployeeNameof"Mohan"updatedintheEmployeecollection.

Tocheckthatthedatahasbeenproperlyupdatedinthedatabase,youneedtoexecutethefollowingcommandsinMongoDB

1. UseEmployeeDB2. db.Employee.find({Employeeid:4})

ThefirststatementensuresthatyouareconnectedtotheEmployeeDbdatabase.Thesecondstatementsearchesfortherecordwhichhastheemployeeidof4.

6. Deletingdocumentsinacollection-Documentscanbedeletedinacollectionusingthe"deleteOne"methodprovidedbytheMongoDBlibrary.ThebelowcodesnippetshowshowtodeleteadocumentinamongoDBcollection.




db.collection('Employee').deleteOne(

{


}

);

});

CodeExplanation:

1. Hereweareusingthe"deleteOne"methodfromtheMongoDBlibrary,whichisusedtodeleteadocumentinamongoDBcollection.

2. Wearespecifyingthesearchcriteriaofwhichdocumentneedstobedeleted.Inourcase,wewanttofindthedocumentwhichhastheEmployeeNameof"Mohan"anddeletethisdocument.

IfyounowcheckthecontentsofyourMongoDBdatabase,youwillfindtherecordwithEmployeeidof4andEmployeeNameof"Mohan"deletedfromtheEmployeecollection.

Tocheckthatthedatahasbeenproperlyupdatedinthedatabase,youneedtoexecutethefollowingcommandsinMongoDB

1. UseEmployeeDB2. db.Employee.find()

ThefirststatementensuresthatyouareconnectedtotheEmployeeDbdatabase.Thesecondstatementsearchesanddisplayalloftherecordsintheemployeecollection.Hereyoucanseeiftherecordhasbeendeletedornot.

HowtobuildanodeexpressappwithMongoDBtostoreandservecontentBuildinganapplicationwithacombinationofbothusingexpressandMongoDBisquitecommonnowadays.

WhenworkingwithJavaScriptwebbasedapplications,onewillnormallyhereofthetermMEANstack.

ThetermMEANstackreferstoacollectionofJavaScriptbasedtechnologiesusedtodevelopwebapplications.MEANisanacronymforMongoDB,ExpressJS,AngularJSandNode.js.

Hence,it'salwaysgoodtounderstandhowNode.jsandMongoDBworktogethertodeliverapplicationswhichinteractwithbackenddatabases.

Let'slookatasimpleexampleofhowwecanuse"express"and"MongoDB"together.OurexamplewillmakeuseofthesameEmployeecollectionintheMongoDBEmployeeDBdatabase.

WewillnowincorporateExpresstodisplaythedataonourwebpagewhenitisrequestedbytheuser.WhenourapplicationrunsonNode.js,onemightneedtobrowsetotheURLhttp://localhost:3000/Employeeid.

Whenthepageislaunched,alltheemployeeidintheEmployeecollectionwillbedisplayed.Solet'sseethecodesnippetinsectionswhichwillallowustoachievethis.

Step1)Defineallthelibrarieswhichneedtobeusedinourapplication,whichinourcaseisboththeMongoDBandexpresslibrary.

CodeExplanation:

1. Wearedefiningour'express'library,whichwillbeusedinourapplication.2. Wearedefiningour'express'library,whichwillbeusedinourapplicationforconnecting

toourMongoDBdatabase.3. HerewearedefiningtheURLofourdatabasetoconnectto.4. Finally,wearedefiningastringwhichwillbeusedtostoreourcollectionofemployeeid

whichneedtobedisplayedinthebrowserlateron.

Step2)Inthisstep,wearenowgoingtogetalloftherecordsinour'Employee'collectionandworkwiththemaccordingly.

CodeExplanation:

1. Wearecreatingaroutetoourapplicationcalled'Employeeid.'Sowheneveranybodybrowsestohttp://localhost:3000/Employeeidofourapplication,thecodesnippetdefinedforthisroutewillbeexecuted.

2. Herewearegettingalloftherecordsinour'Employee'collectionthroughthedb.collection('Employee').find()command.Wearethenassigningthiscollectiontoavariablecalledcursor.Usingthiscursorvariable,wewillbeabletobrowsethroughalloftherecordsofthecollection.

3. Wearenowusingthecursor.each()functiontonavigatethroughalloftherecordsofourcollection.Foreachrecord,wearegoingtodefineacodesnippetonwhattodowheneachrecordisaccessed.

4. Finally,weseethatiftherecordreturnedisnotnull,thenwearetakingtheemployeeviathecommand"item.Employeeid".TherestofthecodeisjusttoconstructaproperHTMLcodewhichwillallowourresultstobedisplayedproperlyinthebrowser.

Step3)Inthisstep,wearegoingtosendouroutputtothewebpageandmakeourapplicationlistenonaparticularport.

CodeExplanation:

1. Herewearesendingtheentirecontentwhichwasconstructedintheearliersteptoourwebpage.The'res'parameterallowsustosendcontenttoourwebpageasaresponse.

2. WearemakingourentireNode.jsapplicationlistenonport3000.

Output:

Fromtheoutput,

Itclearlyshowsthatalloftheemployeeid'sintheEmployeecollectionwereretrieved.ThisisbecauseweusetheMongoDBdrivertoconnecttothedatabaseandretrievealltheEmployeerecordsandsubsequentlyused"express"todisplaytherecords.



varapp=express();



varstr="";

app.route('/Employeeid').get(function(req,res)

{


varcursor=db.collection('Employee').find();

//noinspectionJSDeprecatedSymbols

cursor.each(function(err,item){

if(item!=null){

str=str+"Employeeid"+item.Employeeid+"";

}

});

res.send(str);

db.close();

});

});


Note:cursor.eachmaybedeprecatedbasedonversionofyourMongoDBdriver.Youcanappend//noinspectionJSDeprecatedSymbolsbeforecursor.eachtocircumventtheissue.Alternatively,youcanuseforEach.BelowisthesamplecodeusingforEach


varapp=express();



varstr="";

app.route('/Employeeid').get(function(req,res){


varcollection=db.collection('Employee');

varcursor=collection.find({});

str="";

cursor.forEach(function(item){

if(item!=null){

str=str+"Employeeid"+item.Employeeid+"";

}

},function(err){

res.send(str);

db.close();

}

);

});

});


Summary

Node.jsisusedinconjunctionwithNoSQLdatabasestobuildalotofmoderndayswebapplications.SomeofthecommondatabasesusedareMySQLandMongoDB.OneofthecommonmodulesusedforworkingwithMongoDBdatabasesisamodulecalled'MongoDB.'ThismoduleisinstalledviatheNodepackagemanager.WiththeMongoDBmodule,it'spossibletoqueryforrecordsinacollectionandperformthenormalupdate,deleteandinsertoperations.Finally,oneofthemodernpracticesistousetheexpressframeworkalongwithMongoDBtodelivermoderndayapplications.TheExpressframeworkcanmakeuseofthedatareturnedbytheMongoDBdriveranddisplaythedatatotheuserinthewebpageaccordingly.

Chapter7:Promise,Generator,EventandFilestream

Inprevioustutorials,youwouldhaveseencallbackfunctionswhichareusedforAsynchronousevents.Butsometimescallbackfunctionscanbecomeanightmarewhentheystartbecomingnested,andtheprogramstartstobecomelongandcomplex.

Insuchcases,Node.jsprovidesadditionalfeaturestorectifyproblemswhichareencounteredwhenusingcallbacks.TheseareclassifiedintoPromises,generatesandevents.Duringthecourseofthistutorial,wewilllearnandseetheseconceptsinfurtherdetail.

WhatarepromisesBeforewestartwithpromises,let'sfirstrevisitwhatare"callback"functionsinNode.js.Wehaveseenthesecallbackfunctionsalotinthepreviouschapters,solet'squicklygothroughoneofthem.

Theexamplebelowshowsacodesnippet,whichisusedtoconnecttoaMongoDBdatabaseandperformanupdateoperationononeoftherecordsinthedatabase.

1. Intheabovecode,thepartofthefunction(err,db)isknownasthedeclarationofananonymousorcallbackfunction.WhentheMongoClientcreatesaconnectiontotheMongoDBdatabase,itwillreturntothecallbackfunctiononcetheconnectionoperationiscompleted.Soinasense,theconnectionoperationshappensinthebackground,andwhenitisdone,itcallsourcallbackfunction.RememberthatthisisoneofthekeypointsofNode.jstoallowmanyoperationstohappenconcurrentlyandthusnotblockanyuserfromperforminganoperation.

2. Thesecondcodeblockiswhatgetsexecutedwhenthecallbackfunctionisactuallycalled.ThecallbackfunctionjustupdatesonerecordinourMongoDBdatabase.

Sowhatisapromisethen?Well,apromiseisjustanenhancementtocallbackfunctionsinNode.js.Duringthedevelopmentlifecycle,theremaybeaninstancewhereyouwouldneedto

nestmultiplecallbackfunctionstogether.Thiscangetkindofmessyanddifficulttomaintainatacertainpointintime.Inshort,apromiseisanenhancementtocallbacksthatlookstowardsalleviatingtheseproblems.

Thebasicsyntaxofapromiseisshownbelow;

varpromise=doSomethingAync()

promise.then(onFulfilled,onRejected)

"doSomethingAync"isanycallbackorasynchronousfunctionwhichdoessomesortofprocessing.Thistime,whendefiningthecallback,thereisavaluewhichisreturnedcalleda"promise."Whenapromiseisreturned,itcanhave2outputs.Thisisdefinedbythe'thenclause'.Eithertheoperationcanbeasuccesswhichisdenotedbythe'onFulfilled'parameter.Oritcanhaveanerrorwhichisdenotedbythe'onRejected'parameter.

Note:Sothekeyaspectofapromiseisthereturnvalue.ThereisnoconceptofareturnvaluewhenworkingwithnormalcallbacksinNode.js.Becauseofthereturnvalue,wehavemorecontrolofhowthecallbackfunctioncanbedefined.

Inthenexttopic,wewillseeanexampleofpromisesandhowtheybenefitfromcallbacks.

CallbackstopromisesNowlet'slookatanexampleofhowwecanuse"promises"fromwithinaNode.jsapplication.InordertousepromisesinaNode.jsapplication,the'promise'modulemustfirstbedownloadedandinstalled.

Wewillthenmodifyourcodeasshownbelow,whichupdatesanEmployeenameinthe'Employee'collectionbyusingpromises.

Step1)InstallingtheNPMModules

TousePromisesfromwithinaNodeJSapplication,thepromisemoduleisrequired.Toinstallthepromisemodule,runthebelowcommand

npminstallpromise

Step2)Modifythecodetoincludepromises

varPromise=require('promise');



MongoClient.connect(url)

.then(function(err,db){

db.collection('Employee').updateOne({

"EmployeeName":"Martin"

},{

$set:{


}

});

});

CodeExplanation:-

1. Thefirstpartistoincludethe'promise'modulewhichwillallowustousethepromisefunctionalityinourcode.

2. Wecannowappendthe'then'functiontoourMongoClient.connectfunction.Sowhatthisdoesisthatwhentheconnectionisestablishedtothedatabase,weneedtoexecutethecodesnippetdefinedthereafter.

3. Finally,wedefineourcodesnippetwhichdoestheworkofupdatingEmployeeNameoftheemployeewiththenameof"Martin"to"Mohan".

Note:-

IfyounowcheckthecontentsofyourMongoDBdatabase,youwillfindthatifarecordwithEmployeeNameof"Martin"exists,itwillbeupdatedto"Mohan."

Tocheckthatthedatahasbeenproperlyinsertedinthedatabase,youneedtoexecutethefollowingcommandsinMongoDB

1. UseEmployeeDB2. db.Employee.find({EmployeeName:Mohan})

ThefirststatementensuresthatyouareconnectedtotheEmployeeDbdatabase.Thesecondstatementsearchesfortherecordwhichhastheemployeenameof"Mohan".

DealingwithnestedpromisesWhendefiningpromises,itneedstobenotedthatthe"then"methoditselfreturnsapromise.Soinasense,promisescanbenestedorchainedtoeachother.

Intheexamplebelow,weusechainingtodefine2callbackfunctions,bothofwhichinsertarecordintotheMongoDBdatabase.

(Note:Chainingisaconceptusedtolinkexecutionofmethodstooneanother.Supposeifyourapplicationhad2methodscalled'methodA'and'methodB.'Andthelogicwassuchthat'methodB'shouldbecalledafter'methodA,'thenyouwouldchaintheexecutioninsuchawaythat'methodB'getscalleddirectlyafter'methodA.')

Thekeythingtonoteinthisexampleisthatthecodebecomescleaner,readableandmaintainablebyusingnestedpromises.

varPromise=require('promise');



MongoClient.connect(url)

.then(function(db){

db.collection('Employee').insertOne({

Employeeid:4,

EmployeeName:"NewEmployee"

})

.then(function(db1){

db1.collection('Employee').insertOne({

Employeeid:5,

EmployeeName:"NewEmployee1"

})

})

});

CodeExplanation:-

1. Wearenowdefining2"then"clauseswhichgetexecutedoneaftertheother.Inthefirstthenclause,wearepassingthe'db'parameterwhichcontainsourdatabaseconnection.Wearethenusingthecollectionpropertyofthe'db'connectiontoinsertrecordsintothe'Employee'collection.The'insertOne'methodisusedtoinserttheactualdocumentintotheEmployeecollection.

2. Wearethenusingthe2ndthenclausealsotoinsertanotherrecordintothedatabase.

IfyounowcheckthecontentsofyourMongoDBdatabase,youwillfindthe2record'sinsertedintotheMongoDBdatabase.

GeneratingpromiseswiththeBlueBirdlibraryBluebirdisafully-featuredPromiselibraryforJavaScript.ThestrongestfeatureofBluebirdisthatitallowsyouto"promisify"otherNodemodulesinordertousethemasynchronously.Promisifyisaconceptappliedtocallbackfunctions.Thisconceptisusedtoensurethateverycallbackfunctionwhichiscalledreturnssomesortofvalue.

SoifaNodeJSmodulecontainsacallbackfunctionwhichdoesnotreturnavalue,ifwePromisifythenodemodule,allthefunction'sinthatspecificnodemodulewouldautomaticallybemodifiedtoensurethatitreturnsavalue.

SoyoucanuseBlueBirdtomaketheMongoDBmodulerunasynchronously.ThisjustaddsanotherlevelofeasewhenwritingNode.jsapplications.

Wewilllookatanexampleofhowtousethebluebirdmodule.

Ourexamplewillfirstestablishaconnectiontothe"Employeecollection"inthe"EmployeeDB"database.If"then"connectionisestablished,thenitwillgetalloftherecordsinthecollectionanddisplaythemintheconsoleaccordingly.


TouseBluebirdfromwithinaNodeapplication,theBluebirdmoduleisrequired.ToinstalltheBluebirdmodule,runthebelowcommand

npminstallbluebird

Step2)ThenextstepistoincludethebluebirdmoduleinyourcodeandpromisifytheentireMongoDBmodule.Bypromisify,wemeanthatbluebirdwillensurethateachandeverymethoddefinedintheMongoDBlibraryreturnsapromise.

CodeExplanation:-

1. TherequirecommandisusedtoincludetheBluebirdlibrary.2. UseBluebird's.promisifyAll()methodtocreateanasyncversionofeverymethodthe

MongoDBmoduleprovides.ThisensuresthateachmethodoftheMongoDBmodulewillruninthebackgroundandensurethatapromiseisreturnedforeachmethodcallintheMongoDBlibrary.

Step3)Thefinalstepistoconnecttoourdatabase,retrievealltherecordsinourcollectionanddisplaytheminourconsolelog.

CodeExplanation:-

1. Youwillnoticethatweareusingthe"connectAsync"methodinsteadofthenormalconnectionmethodforconnectingtothedatabase.BluebirdactuallyaddstheAsynckeywordtoeachmethodintheMongoDBlibrarytodistinguishthosecallswhichreturnpromisesandthosewhichdon't.SothereisnoguaranteethatmethodswithouttheAsyncwordwillreturnavalue.

2. SimilartotheconnectAsyncmethod,wearenowusingthefindAsyncmethodtoreturnalloftherecordsinthemongoDB'Employee'collection.

3. Finally,ifthefindAsyncreturnsasuccessfulpromisewethendefineablockofcodetoiteratethrougheachrecordinthecollectionanddisplaythemintheconsolelog.

Iftheabovestepsarecarriedoutproperly,allofthedocumentsintheEmployeecollectionwillbedisplayedintheconsoleasshownintheoutputbelow.


varPromise=require('bluebird');

varmongoClient=Promise.promisifyAll(require('mongodb')).MongoClient;


mongoClient.connectAsync('mongodb://localhost/EmployeeDB')

.then(function(db){

returndb.collection('Employee').findAsync({})

})

.then(function(cursor){

cursor.each(function(err,doc){

console.log(doc);

})

});

CreatingacustompromiseAcustompromisecanbecreatedbyusinganodemodulecalled'q.'The'q'libraryneedstobedownloadedandinstalledusingthenodepackagemanager.Afterusingthe'q'library,themethod"denodeify"canbecalledwhichwillcauseanyfunctiontobecomeafunctionwhichreturnsapromise.

Intheexamplebelow,wewillcreateasimplefunctioncalled"Add"whichwilladd2numbers.Wewillconvertthisfunctionintoafunctiontoreturnapromise.

Oncethatisdone,wewillusethepromisereturnedbytheAddfunctiontodisplayamessageintheconsole.log.

Let'sfollowthebelowstepstocreatingourcustomfunctiontoreturnapromise.


Touse'q'fromwithinaNodeJSapplication,the'q'moduleisrequired.Toinstallthe'q'module,runthebelowcommand

npminstallq

Step2)Definethefollowingcodewhichwillbeusedtocreatethecustompromise.

varQ=require('q');

functionAdd(){

vara,b,c;

a=5;b=6;

c=a+b;

}

varDisplay_promise=Q.denodeify(Add);

varpromise=Add;

promise.then

{console.log("Additionfunctioncomplete");}

CodeExplanation:-

1. Thefirstbitistoincludethe'q'librarybyusingtherequirekeyword.Byusingthislibrary,wewillbeabletodefineanyfunctiontoreturnacallback.

2. WearecreatingafunctioncalledAddwhichwilladd2numbersdefinedinvariablesaandb.Thesumofthesevalueswillbestoredinvariablec.

3. Wearethenusingtheqlibrarytodenodeify(themethodusedtoconvertanyfunctionintoafunctionthatwouldreturnapromise)ourAddfunctionorinotherwiseconvertourAddfunctiontoafunctionwhichreturnsapromise.

4. Wenowcallour"Add"functionandareabletogetareturnpromisevaluebecauseofthepriorstepweperformedofdenodeifytheAddfunction.

5. The'then'keywordisusedspecifythatifthefunctionisexecutedsuccessfullythendisplaythestring"Additionfunctioncompleted"intheconsole.log.

Whentheabovecodeisrun,theoutput"Additionfunctioncompleted"willbedisplayedintheconsole.logasshownbelow.

WhataregeneratorsGeneratorshavebecomequitefamousinNode.jsinrecenttimesandthatprobablybecauseofwhattheyarecapableofdoing.

Generatorsarefunctionexecutionsthatcanbesuspendedandresumedatalaterpoint.Generatorsareusefulwhencarryingoutconceptssuchas'lazyexecution'.Thisbasicallymeansthatbysuspendingexecutionandresumingatwill,weareabletopullvaluesonlywhenweneedto.

Generatorshavethebelow2keymethods

1. Yieldmethod–Theyieldmethodiscalledinafunctiontohalttheexecutionofthefunctionatthespecificlinewheretheyieldmethodiscalled.

2. Nextmethod–Thismethodiscalledfromthemainapplicationtoresumetheexecutionofafunctionwhichhasayieldmethod.Theexecutionofthefunctionwillcontinuetillthenextyieldmethodortilltheendofthemethod.

Let'slookatanexampleofhowgeneratorscanbeused.

Inourexample,wearegoingtohaveasimpleAddfunctionwhichwilladd2numbers,butwewillkeeponhaltingthemethodexecutionatdifferentpointstoshowcasehowgeneratorscanbeused.

function*Add(x){

yieldx+1;

vary=yield(null);

y=6

returnx+y;

}

vargen=Add(5);

gen.next();

gen.next();

CodeExplanation:-

1. Thefirststepistodefineourgenerator"function".Notethatthisisdonebyaddinga"*"tothefunctionkeyword.WearethendefiningafunctioncalledAddwhichtakesa

parameterofx.2. Theyieldkeywordisaspecifictogenerators.Thismakesitapowerfulconstructfor

pausingafunctioninthemiddleofanything.Sohere,thefunctionexecutionwillbehaltedtillweinvokethenext()function,whichwillbedoneinStep4.Atthispoint,thevalueofxwillbecome6andtheexecutionofthefunctionwillbestopped.

3. Thisiswherewefirstcallthegeneratorfunctionandsendthevalueof5toourAddfunction.ThisvaluewillbesubstitutedinthexparameterofourAddfunction.

4. Oncewecallthenext()function,theAdd()functionwillresumetheexecution.Whenthenextstatementvary=yield(null)willbeexecuted,theAdd()functionwillagainstopexecuting.

5. Nowaftercallingthenext()functionagain,thenextstatementswillrun,andthecombinedvalueofx=6andy=6willbeaddedandreturned.

Callbacksvs.generatorsGeneratorsareusedtosolvetheproblemofwhatisknownascallbackhell.SometimescallbackfunctionsbecomesonestedduringthedevelopmentofaNode.jsapplicationthatitjustbecomestoocomplicatedtousecallbackfunctions.

Thisiswheregeneratorsareuseful.Oneofthemostcommonexamplesofthisiswhencreatingtimerfunctions.

Let'sseethebelowexampleofhowgeneratorscanprovetobeusefulovercallbacks.

Ourexamplewilljustcreateasimpletimedelayfunction.Wewouldthenwanttocallthisfunctionincorporatingadelayof1000,2000and3000ms.

Step1)Defineourcallbackfunctionwiththenecessarytimedelaycode.

CodeExplanation:-

1. HerewearecreatingafunctioncalledTimedelaywithaparametercalledptime.Thiswilltakeinthenecessarytimedelaywewanttointroduceinourapplication.

2. Thenextstepistojustcreateamessage,whichwillbedisplayedtotheusersayingthattheapplicationisgoingtobepauseforthesemanynumbersofmilliseconds.

Step2)Nowlet'slookatthecodeifwewereincorporatingcallbacks.Supposewewantedtoincorporatecallbacksbasedonthevalueof1000,2000and3000milliseconds,thebelowcodeshowshowwewouldneedtoimplementtheseusingcallbacks.

CodeExplanation:-

1. WearecallingtheTimedelayasacallbackwith1000asthevalue.2. NextwewanttocalltheTimedelayfunctionagainwith2000asthevalue.3. Finally,wewanttocalltheTimedelayfunctionagainwith3000asthevalue.

Fromtheabovecode,youcanseethatitbecomesmessieraswewanttostartcallingthefunctionmultipletimes.

Step3)Nowlet'sseehowtoimplementthesamecodeusinggenerators.FromthebelowcodeyoucannowseehowsimpleithasbecometoimplementtheTimedelayfunctionusinggenerators.

CodeExplanation:-

1. WearefirstdefiningageneratorfunctionwhichwillbeusedtocallourTimedelayfunction.

2. WearecallingtheYieldfunctionalongwiththeTimedelayfunctionwith1000astheparametervalue.

3. WearethencallingtheYieldfunctionalongwiththeTimedelayfunctionwith2000astheparametervalue.

4. Finally,wearecallingtheYieldfunctionalongwiththeTimedelayfunctionwith3000astheparametervalue.

FilestreaminNode.jsNodemakesextensiveuseofstreamsasadatatransfermechanism.

Forexample,whenyououtputanythingtotheconsoleusingtheconsole.logfunction,youareactuallyusingastreamtosendthedatatotheconsole.

Node.jsalsohastheabilitytostreamdatafromfilessothattheycanbereadandwrittenappropriately.Wewillnowlookatanexampleofhowwecanusestreamstoreadandwritefromfiles.Weneedtofollowthebelow-mentionedstepsforthisexample

Step1)Createafilecalleddata.txtwhichhasthebelowdata.LetassumethisfileisstoredontheDdriveofourlocalmachine.

TutorialonNode.js

Introduction

Events

Generators

DataConnectivity

UsingJasmine

Step2)Writetherelevantcodewhichwillmakeuseofstreamstoreaddatafromthefile.

varfs=require("fs");

varstream;

stream=fs.createReadStream("D://data.txt");

stream.on("data",function(data){

varchunk=data.toString();

console.log(chunk);

});

CodeExplanation:-

1. Wefirstneedtoincludethe'fs'moduleswhichcontainallthefunctionalityrequiredtocreatestreams.

2. Nextwecreateareadablestreambyusingthemethod–createReadStream.Asaninput,wegivethelocationofourdata.txtfile.

3. Thesteam.onfunctionisaneventhandlerandinit,wearespecifyingthefirstparameteras'data.'Thismeansthatwheneverdatacomesinthestreamfromthefile,thenexecuteacallbackfunction.Inourcase,wearedefiningacallbackfunctionwhichwillcarryout2basicsteps.Thefirstistoconvertthedatareadfromthefileasastring.Thesecondwouldbetosendtheconvertedstringasanoutputtotheconsole.

4. Wearetakingeachchunkofdatawhichisreadfromthedatastreamandconvertingittoastring.

5. Finally,wearesendingtheoutputofeachstringconvertedchunktotheconsole.

Output:

Ifthecodeisexecutedproperly,youwillseetheaboveoutputintheconsole.Thisoutputwillbethesameasthatinthedata.txtfile.

Writingtoafile

Inthesameway,thatwecreateareadstream,wecanalsocreateawritestreamtowritedatatoafile.Let'sfirstcreateanemptyfilewithnocontentscalleddata.txt.Let'sassumethisfileisplacedintheDdriveofourcomputer.

Thebelowcodeshowshowwecanwritedatatothefile.

varfs=require("fs");

varstream;

stream=fs.createWriteStream("D://data.txt");

stream.write("TutorialonNode.js")

stream.write("Introduction")

stream.write("Events")

stream.write("Generators")

stream.write("DataConnectivity")

stream.write("UsingJasmine")

CodeExplanation:-

1. Wearecreatingawritablestreambyusingthemethod–createWriteStream.Asaninput,wegivethelocationofourdata.txtfile.

2. Nextweusedthestream.writeamethodtowritethedifferentlinesoftexttoourtextfile.Thestreamwilltakecareofwritingthisdatatothedata.txtfile.

Ifyouopenthedata.txtfile,youwillnowseethefollowingdatainthefile

TutorialonNode.js

Introduction

Events

Generators

DataConnectivity

UsingJasmine

PipesinNode.jsWithinNodeapplications,streamscanbepipedtogetherusingthepipe()method,whichtakestwoarguments:

ARequiredwritablestreamthatactsasthedestinationforthedataandAnoptionalobjectusedtopassinoptions.

Atypicalexampleofusingpipes,ifyouwanttotransferdatafromonefiletotheother.

Solet'sseeanexampleofhowwecantransferdatafromonefiletotheotherusingpipes.

Step1)Createafilecalleddatainput.txtwhichhasthebelowdata.LetassumethisfileisstoredontheDdriveofourlocalmachine.

TutorialonNode.js

Introduction

Events

Generators

DataConnectivity

UsingJasmine

Step2)CreateablankemptyfilecalleddataOutput.txtandplaceditontheDdriveofyourlocalmachine.

Step3)Writethebelowcodetocarryoutthetransferofdatafromthedatainput.txtfiletothedataOutput.txtfile.

CodeExplanation:-

1. Wearefirstcreatinga"readstream"toourdatainput.txtfilewhichcontainsallourdatawhichneedstobetransferredtothenewfile.

2. Wethenneedtocreatea"writestream"toourdataOutput.txtfile,whichisouremptyfileandisthedestinationforthetransferofdatafromthedatainput.txtfile.

3. Wethenusethepipecommandtotransferthedatafromthereadstreamtothewritestream.Thepipecommandwilltakeallthedatawhichcomesintothereadstream,andpushittothewritestream.

IfyounowopenthedataOutput.txtfile,youwillseeallthedatawhichwaspresentinthedatainput.txtfile.

EventsinNode.jsEventsareoneofthekeyconceptsinNode.jsandsometimesNode.jsisreferredtoasanEvent-drivenframework.

Basically,aneventissomethingthathappens.Forexample,ifaconnectionisestablishedtoadatabase,thenthedatabaseconnectioneventistriggered.Eventdrivenprogrammingistocreatefunctionsthatwillbetriggeredwhenspecificeventsaretriggered.

Let'slookatabasicexampleofdefininganeventinNode.js.

Wearegoingtocreateaneventcalled'data_received'.Whenthiseventistriggered,thetext"datareceived"willbesenttotheconsole.

varevents=require('events');

vareventEmitter=newevents.EventEmitter();

eventEmitter.on('data_received',function(){

console.log('datareceivedsuccesfully.');

});

eventEmitter.emit('data_received');

CodeExplanation:-

1. Usetherequirefunctiontoincludethe'events'module.Withthismodule,youwillbeabletocreateeventsinNode.js.

2. Createaneweventsemitter.Thisisusedtobindtheevent,whichinourcaseis"data_received"toacallbackfunctionwhichisdefinedinstep3.

3. Wedefineanevent-drivenfunctionwhichsaysthatifincasethe"data_received"eventistriggeredthenweshouldoutputthetext"data_received"totheconsole.

4. Finally,wedohaveamanualtriggerofoureventusingtheeventEmiter.emitfunction.Thiswilltriggerthedata_receivedevent.

Whentheprogramisrun,thetext"datareceived"willbesenttotheconsoleasshownbelow.

EmittingEventsWhendefiningevents,therearedifferentmethodsforeventswhichcanbeinvoked.Thistopicfocusesonlookingateachoneofthemindetail.

1. Onetimeeventhandlers

Sometimesyoumaybeinterestedinreactingtoaneventonlythefirsttimeitoccurs.Inthesesituations,youcanusetheonce()method.

Let'sseehowwecanmakeuseoftheoncemethodforeventhandlers.

CodeExplanation:-

1. Hereweareusingthe'once'methodtosaythatfortheevent'data_received,'thecallbackfunctionshouldonlybeexecutedonce.

2. Herewearemanuallytriggeringthe'data_received'event.3. Whenthe'data_received'eventistriggeredagain,thistime,nothingwillhappen.Thisis

becauseofthefirststepwherewesaidthattheeventcouldonlybetriggeredonce.

Ifthecodeisexecutedproperly,theoutputinthelogwillbe'data_receivedsuccessfully'.Thismessagewillonlyappearonceintheconsole.

2. InspectingEventListeners

Atanypointinitslifetime,aneventemittercanhavezeroormorelistenersattachedtoit.Thelistenersforeacheventtypecanbeinspectedinseveralways.

Ifyouareinterestedinonlydeterminingthenumberofattachedlisteners,thenlooknofurtherthantheEventEmitter.listenerCount()method.

(Note:Listenersareimportantbecausethemainprogramshouldknowiflistenersarebeingaddedontheflytoanevent,elsetheprogramwillmalfunctionbecauseadditionallistenerswillgetcalled.)

CodeExplanation:-

1. WearedefininganeventEmittertypewhichisrequiredforusingtheevent-relatedmethods.

2. Wearethendefininganobjectcalledemitterwhichwillbeusedtodefineoureventhandlers.

3. Wearecreating2eventshandlerswhichbasicallydonothing.ThisiskeptsimpleforourexamplejusttoshowhowthelistenerCountmethodworks.

4. NowwhenyouinvokethelistenerCountmethodonourdata_receivedevent,itwillsendthenumberofeventlistenersattachedtothiseventintheconsolelog.

Ifthecodeisexecutedproperly,thevalueof2willbeshownintheconsolelog.

3. ThenewListenerEvent

Eachtimeaneweventhandlerisregistered,theeventemitteremitsanewListenerevent.Thiseventisusedtodetectneweventhandlers.YoutypicallyusenewListenereventwhenyouneedtoallocateresourcesorperformsomeactionforeachneweventhandler.

varevents=require('events');

vareventEmitter=events.EventEmitter;

varemitter=neweventEmitter();

emitter.on("newListener",function(eventName,listener){

console.log("Addedlistenerfor"+eventName+"events");

});

emitter.on('data_received',function(){});

emitter.on('data_received',function(){});

CodeExplanation:-

1. Wearecreatinganeweventhandlerforthe'newListener'event.Sowheneveraneweventhandlerisregistered,thetext"Addedlistenerfor"+theeventnamewillbedisplayedintheconsole.

2. Herewearewritingtotheconsolethetext"Addedlistenerfor"+theeventnameforeacheventregistered.

3. Wearedefining2eventhandlersforourevent'data_received'.

Iftheabovecodeisexecutedproperly,thebelowtextwillbeshownintheconsole.Itjustshowsthatthe'newListener'eventhandlerwastriggeredtwice.

Addedlistenerfordata_receivedevents

Addedlistenerfordata_receivedevents

Summary

UsingcallbackfunctionsinNode.jsdoeshaveitsdisadvantages.Sometimesduringtheprocessofdevelopment,thenesteduseofcallbackfunctionscanmakethecodemessieranddifficulttomaintain.Mostoftheissueswithnestedcallbackfunctionscanbemitigatedwiththeuseofpromisesandgeneratorsinnode.jsAPromiseisavaluereturnedbyanasynchronousfunctiontoindicatethecompletionoftheprocessingcarriedoutbytheasynchronousfunction.Promisescanbenestedwithineachothertomakecodelookbetterandeasiertomaintainwhenmanyasynchronousfunctionneedtobecalledatthesametime.Generatorscanalsobeusedtoalleviatetheproblemswithnestedcallbacksandassistinremovingwhatisknownasthecallbackhell.Generatorsareusedtohalttheprocessingofafunction.Thisisaccomplishedbyusageofthe'yield'methodintheasynchronousfunction.StreamsareusedinNode.jstoreadandwritedatafromInput-Outputdevices.Node.jsmakesuseofthe'fs'librarytocreatereadableandwritablestreamstofiles.Thesestreamscanbeusedtoreadandwritedatafromfiles.

Pipescanbeusedtoconnectmultiplestreamstogether.Oneofthemostcommonexampleistopipethereadandwritestreamtogetherforthetransferofdatafromonefiletotheother.Node.jsisoftenalsotaggedasaneventdrivenframework,andit'sveryeasytodefineeventsinNode.js.Functionscanbedefinedwhichrespondtotheseevents.Eventsalsoexposemethodsforrespondingtokeyevents.Forexample,wehaveseentheonce()eventhandlerwhichcanbeusedtomakesurethatacallbackfunctionisonlyexecutedoncewhenaneventistriggered.

Chapter8:TestingwithJasmine

Testingisakeyelementtoanyapplication.ForNode.js,theframeworkavailablefortestingiscalledJasmine.Inearly2000,therewasaframeworkfortestingjavascriptapplicationscalledJsUnit.Laterthisframeworkgotupgradedandisnowknownasjasmine.

Jasminehelpsinautomatedunittesting,somethingwhichhasbecomequiteakeypracticewhendevelopinganddeployingmoderndaywebapplications.

Inthistutorial,youwilllearnhowtogetyourenvironmentsetupwithjasmineandhowyoucanstarttestingyourfirstNode.jsapplicationwithjasmine.

OverviewofJasminefortestingNode.jsapplicationsJasmineisaBehaviorDrivenDevelopment(BDD)testingframeworkforJavaScript.Itdoesnotrelyonbrowsers,DOM,oranyJavaScriptframework.Thus,it'ssuitedforwebsites,Node.jsprojects,oranywherethatJavaScriptcanrun.TostartusingJasmine,youneedtofirstdownloadandinstallthenecessaryJasminemodules.

Nextyouwouldneedtoinitializeyourenvironmentandinspectthejasmineconfigurationfile.ThebelowstepsshowshowtosetupJasmineinyourenvironment


TousethejasmineframeworkfromwithinaNodeapplication,thejasminemoduleneedstobeinstalledfirst.Toinstallthejasmine-nodemodule,runthebelowcommand.

npminstalljasmine-node

Step2)Initializingtheproject–Bydoingthis,jasminecreatesaspecdirectoryandconfigurationjsonforyou.Thespecdirectoryisusedtostoreallyourtestfiles.Bydoingthis,jasminewillknowwhereallyourtestsare,andthencanexecutethemaccordingly.TheJSONfileisusedtostorespecificconfigurationinformationaboutjasmine.

Toinitializethejasmineenvironment,runthebelowcommand

jasmineinit

Step3)Inspectyourconfigurationfile.Theconfigurationfilewillbestoredinthespec/supportfolderasjasmine.json.ThisfileenumeratesthesourcefilesandspecfilesyouwouldliketheJasminerunnertoinclude.

Thebelowscreenshotshowsatypicalexampleofthepackage.jsonfileforjasmine.

1. Notethatthespecdirectoryisspecifiedhere.Asnotedearlier,whenjasminerunsitsearchesforalltestsinthisdirectory.

2. Thenextthingtonoteisthespec_filesparameter–Thisdenotesthatwhatevertestfilesarecreatedtheyshouldbeappendedwiththe'spec'keyword.

HowtouseJasminetotestNode.jsapplicationsInordertouseJasminetotestNode.jsapplications,aseriesofstepsneedstobefollowed.

Inourexamplebelow,wearegoingtodefineamodulewhichadd2numberswhichneedtobetested.WewillthendefineaseparatecodefilewiththetestcodeandthenusejasminetotesttheAddfunctionaccordingly.

Step1)Definethecodewhichneedstobetested.Wearegoingtodefineafunctionwhichwilladd2numbersandreturntheresult.Thiscodeisgoingtobewritteninafilecalled"Add.js."


exports.AddNumber=function(a,b)

{

returna+b;

};

CodeExplanation:

1. The"exports"keywordisusedtoensurethatthefunctionalitydefinedinthisfilecanactuallybeaccessedbyotherfiles.

2. Wearethendefiningafunctioncalled'AddNumber.'Thisfunctionisdefinedtotake2parameters,aandb.Thefunctionisaddedtothemodule"exports"tomakethefunctionasapublicfunctionthatcanbeaccessedbyotherapplicationmodules.

3. Wearefinallymakingourfunctionreturntheaddedvalueoftheparameters.

Step2)Nextweneedtodefineourjasminetestcodewhichwillbeusedtotestour"Add"functionIntheAdd.jsfile.Thebelowcodeneedstoputinafilecalledadd-spec.js.

Note:-Theword'spec'needstobeaddedtothetestfilesothatitcanbedetectedbyjasmine.

varapp=require("../Add.js");

describe("Addition",function(){

it("Thefunctionshouldadd2numbers",function(){

varvalue=app.AddNumber(5,6);

expect(value).toBe(11);

});

});

CodeExplanation:

1. WeneedtofirstincludeourAdd.jsfilesothatwecantestthe'AddNumber'functioninthisfile.

2. Wearenowcreatingourtestmodule.Thefirstpartofthetestmoduleistodescribeamethodwhichbasicallygivesanameforourtest.Inthiscase,thenameofourtestis"Addition".

3. Thenextbitistogiveadescriptionforourtestusingthe'it'method.4. WenowinvokeourAddnumbermethodandsendin2parameters5and6.Thiswillbe

passedtoourAddnumbermethodintheApp.jsfile.Thereturnvalueisthenstoredinavariablecalledvalue.

5. Thefinalstepistodothecomparisonorouractualtest.SinceweexpectthevaluereturnedbytheAddnumberfunctiontobe11,wedefinethisusingthemethodexpect(value).toBe(theexpectedvalue).

Output

1. Inordertorunthetest,oneneedstorunthecommandjasmine.2. Thebelowscreenshotshowsthatafterthejasminecommandisrun,itwilldetectthat

thereisatestcalledadd-spec.jsandexecutethattestaccordingly.Ifthereareanyerrorsinthetest,itwillbeshownaccordingly.

Summary

InordertotestaNode.jsapplication,thejasmineframeworkneedstobeinstalledfirst.ThisisdonebyusingtheNodepackagemanager.Thetestcodeneedstobewritteninaseparatefile,andtheword'spec'shouldbeappendedtothefilename.Onlyifthisisdonewilljasminebeabletodetectthatafileneedstoberun.Torunthetest,youneedtoexecutethejasminecommand.Thiswillfindallfileswhichhavethe'spec'wordattachedtoitandrunthefileaccordingly.

OneLastThing….

DIDYOUENJOYTHEBOOK?IFSO,THENLETMEKNOWLEAVINGAREVIEWONAMAZON!Reviewsarelifebloodofindependentauthors.Iwouldappreciateevenafewwordsandratingifthat’sallyouhavetimefor

IFYOUDIDNOTLIKETHISBOOK,THENPLEASETELLME!EMAILmeandLetmeknowwhatyoudidn’tlike!PerphaseIcanchangeit.Intoday’sworldabookdoesn’thavetobestagnant,itcanimprovewithtimeandfeedbackfromreaderslikeyou.Youcanimpactthisbook,andIwelcomeyourfeedback.Helpmakethisbookbetterforeveryone!

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