regular expressions cse 33451. regex links mdn regular expressions regexpal

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Regular Expressions

Regex Links

• MDN Regular Expressions

• Regexpal

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Regular Expressions

• Patterns used to match character combinations in strings.

• In JS, regular expressions can be used with the RegExp object and with the String object.

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Regex Use Cases

• Find and extract data from a document.

• Validate content supplied in a form before it is submitted.– Telephone numbers– SSN– Email addresses– Anything that follows a pattern

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Regex Syntax

• Regular expressions are an extremely powerful tool implemented in most languages; however…

• Regular expressions have their own syntax and usage of special characters.

• Difficult to remember if you use them infrequently.

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Regex Special Characters: ^

Regex: ^AMatches: “Aaaann Animal Named Alex”Doesn’t match: “an A”

Character Meaning

^ Matches the beginning of input

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Regex Special Characters: $

Regex: t$Matches: “Today I ate a tart”Doesn’t match: “tart is here”

Character Meaning

$ Matches the end of input

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Regex Special Characters: *

Regex: a*Matches: “aaaaaaaaaaaaaallred”Matches: “tart”Doesn’t match: “tom”

//Star and Question Mark Characters are useful for the patterns with some variation.

Regex: a*mMatches: “tom”*Novice users often overuse/misuse this character.*

Character Meaning

* Matches the preceding character 0 or more times.

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Regex Special Characters: +

Regex: 1+Matches: “911”Matches: “912”Doesn’t match: “8675309”

Character Meaning

+ Matches the preceding character 1 or more times.

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Regex Special Characters: ?

Regex: l?Matches: “lily”Matches: “llog”Doesn’t match: “Ron”

Character Meaning

? Matches the preceding character 0 or 1 more times.

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Regex Special Characters: .

Regex: .nMatches: “nay, an apple is on the tree”Doesn’t match: “nay, an apple is on the tree”

Character Meaning

. (The decimal point) matches any single character except the newline character.

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Regex Special Characters: |

Regex: red|blueMatches: “hand me that blue crayon”Matches: “hand me that red crayon”Doesn’t match: “hand me that black crayon”

Character Meaning

| Matches one pattern or the other

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Regex Syntax: {n}

Regex: a{2}Matches: “Caandy”Matches: “Caaandy”Doesn’t match: “Candy”

Syntax Meaning

{n} Where n is a positive number. Matches exactly n occurrences.

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Regex Syntax: {n,m}

Regex: a{1,3}Matches: “Candy”Matches: “Caaandy”Matches: “Caaaandy”Doesn’t match: “Cndy”

Syntax Meaning

{n,m} Where n and m are positive integers. Matches at least n and at most m occurrences of the preceding character. When either n or m is zero, it can be omitted.

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Regex Syntax: [xyz]

Regex: [a-d]Matches: “candy”Matches: “brisket”

Syntax Meaning

[xyz] Character set. Matches any one of the enclosed characters.

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Regex Syntax: [xyz]

Regex: [0-5]Matches: “0123456789”Matches: “543210”

Syntax Meaning

[xyz] Character set. Matches any one of the enclosed characters.

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Regex and JavascriptMethod Description

test A RegExp method that tests for a match in a string. It returns true or false.

match A String method that executes a search for a match in a string. It returns an array of information or null on a mismatch.

search A String method that tests for a match in a string. It returns the index of the match, or -1 if the search fails.

replace A String method that executes a search for a match in a string, and replaces the matched substring with a replacement substring.

split A String method that uses a regular expression or a fixed string to break a string into an array of substrings.

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Sample Regex

• To use a regex in javascript, surround the regex with forward slashes

• For example, I have the regex [a-z]. To use it in javascript I would do the following.

var regex = /[a-z]/; //matches any lower case character that is in the alphabet a-z.

var string = "tom";

string.match(regex); // ["t"]

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Advanced Regex FlagsRegular expression have four optional flags that allow for global and case insensitive searching. These flags can be used separately or together in any order, and are included as part of the regex.

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Advanced Regex Flags Example

"tom".match(/T/); // null

//Using the i flag you can perform case insensitive searches.

"tom".match(/T/i); // ["t"/

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Regex Challenge

• Write a regular expression that will only accept a string that contains

• lower and upper case alphabet characters• Underscore characters• Must have an inclusive length between 8 and

32.

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XMLHttpRequest Reference Links

• MDN

• Jibbering.com

• OpenJS XMLHttpRequest Example

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AJAX Quickfacts

• Using the XMLHttpRequest API is what is known as AJAX.

• Asynchronous Javascript and XML.

• Used to send data back and forth from client to server without leaving a webpage.

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AJAX Quick facts

• AJAX is the combination of HTML, CSS, and Javascript.

• Makes sending HTTP request fast and easy.

• Wasn’t very popular until Microsoft’s Outlook Web Access (2000) and Google’s Google Maps(2005) and Gmail(2004).

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How AJAX Works

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Creating an XMLHttpRequest()

• Older browsers, IE5 and IE6, use a different method.

• Newer browsers do the following:

var request = new XMLHttpRequest();

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Initialize a request

• Use the open() method to initialize a request.

//open() interface

void open(DOMString method, DOMString url, optional boolean async, optional DOMString user, optional DOMString password);

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open() : Required Parameters

1. method - The HTTP method to use, such as "GET", "POST", "PUT", "DELETE", etc.

2. url - The URL to which to send the request.

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open() : Optional Parameters

3. async - An optional boolean parameter, defaulting to true, indicating whether or not to perform the operation asynchronously. If this value is false, the send()method does not return until the response is received.

4. user - The optional user name to use for authentication purposes; by default, this is an empty string.

5. password - The optional password to use for authentication purposes; by default, this is an empty string.

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open() examplevar request = new XMLHttpRequest();request.open("GET", "www.google.com", false);

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Send the requestvar request = new XMLHttpRequest();request.open("GET", "www.google.com", false);request.send();

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Handling a response message

• When the server receives the client request, it will perform any necessary actions and return back to the client a response message.

• In most cases, the only handling required is to check the response status code, and if everything is okay access the responseText.

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Handling a response messagevar request = new XMLHttpRequest();request.open("GET", "www.google.com", false);request.send();

if (request.status === 200) { //200 is an HTTP status code. console.log(request.responseText); //print resp txt to console}

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Response Messages attributes/methods

1. status – returns HTTP Status code

2. statusText – returns HTTP status text

3. getResponseHeader() – get specified header from response message.

4. getAllResponseHeaders() – get all headers from response message.

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Handling a response message

5. responseType – returns the format the response is in: "arraybuffer", "blob", "document", "json", and "text“.

6. response – returns of the response entity body.

7. responseText – returns the text of the response entity body.

8. responseXML – returns a DOM object of an xml document.

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Your Turn

• Using this fiddle as basis, make an XMLHttpRequest to http://lyle.smu.edu/~craley/3345/http/showResponse.php.

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Using Query Parameters

• If you recall, GET and POST requests can send a key-value name pair along with an HTTP request.

• This is useful for adding query parameters to your request.

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Query Parameters Example

A typical example would look like this:

name=Tim&lastname=Drake&age=17&alias=Robin

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GET Request

• When sending a GET request, you combine the url with query parameters separated by a question mark.

http://www.google.com?name=Tim&lastname=Drake&age=17&alias=Robin

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GET Request with Query Parms in JS

var url = 'http://www.google.com';var parms = 'name=Tim&lastname=Drake&age=17&alias=Robin';request.open('GET', url+"?"+parms, false);request.send();

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POST Request

• When sending a POST request, the HTTP Message includes the query parameters as apart of the message body.

• Additional information about the query parameters are sent as header info:– Content type– Content length– Etc

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POST Request with Query Parms in JS

var url = 'http://www.google.com';var parms = 'name=Tim&lastname=Drake&age=17&alias=Robin';request.open('POST', url, false);

//Send the proper header information along with the request.

//Depending on the data type (xml, json, etc) you would modify the content type header.request.setRequestHeader("Content-type", "application/x-www-form-urlencoded");request.send(parms);

See jsFiddle

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Full XMLHttpRequest Example

• http://lyle.smu.edu/~craley/3345/http/httpRequest.html

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Synchronous Requests

• So far we’ve only seen synchronous requests.

• These requests pause code execution and wait until a response is given from the server before continuing.

• Depending on the request you could be paused for a long time.

• Not ideal for practical purposes.

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Asynchronous Requests

• These requests provide a callback function that is triggered when the server responds.

• Code execution isn’t paused.

• This is what you should be using in your code.

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Async XMLHttpRequest Examplevar url = "http://www.google.com";var request = new XMLHttpRequest();

request.onreadystatechange = function() {//readyState === 0 : UNSENT. Means open() hasn't been called//readyState === 1 : OPENED. Means send() hasn't been called//readyState === 2 : HEADERS_RECEIVED. Means send() has been called //and headers have been received//readyState === 3 : LOADING. Means downloading //readyState === 4 : DONE. The operation is complete

if (request.readyState === 4) { document.body.innerHTML = request.responseText; }}request.open('GET', url, true); request.send();

See jsFiddle

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XMLHttpRequest Bummer

• Unless you have been given permission, you cannot successfully make an HTTP Request to another server.– Cross Domain Request

• Work arounds for this are– Use a different scripting language (PHP, Python)– Use JSONP– If you have access to the different sever, you can get

Cross Domain Request permission.

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JSON Reference Links

• JSONLint – a JSON validator

• MDN

• JSON.org

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JSON Quick facts

• JSON – javascript object notation

• JSON is a collection of name value pairs

• Is a data-exchange format.

• Closely resembles Javascript syntax.

• Can parse JSON into a JS object.

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Hello World JSON Example

{ “fname" : “bruce" }

1. All JSON data starts and ends with a curly brace or square brace2. The curly brace is what encapsulates the data into an Object.3. After all, JSON stands for Javascript Object Notation.

Object

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Hello World JSON Example

{ “fname" : “bruce" }

name value

pair

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Hello World JSON Example

{ “fname" : “bruce" }

name value

pair

The name portion of the pair must ALWAYS be a String.

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Hello World JSON Example

{ “fname" : “bruce" }

valuename

pair

The value portion of the pair can be several different types.

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Value types

1. numbers2. booleans3. Strings4. null5. arrays (ordered sequences of values)

6. objects (string-value mappings) composed of these values (or of other arrays and objects).

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JSON Example

{ "age": 21, "name": "Sandra Dee", "alive": false}

• It is necessary to separate each pair with a comma. Your JSON will be invalid if you don’t.

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JSON Array Example{ "scores": [ 100, 89, 99, 75]}

• An array is an ordered collection of values.

• An array begins with a [ (left bracket) and ends with ] (right bracket).

• Values are separated by a , (comma).

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Object in JSON

• Just like typical Object-Oriented Programming, you can have objects inside of objects

{ “pizza” : {

“name” : “The Heart Attack”, “id” : 20121,“toppings” : [ “Pepperoni”, “Cheese”, “Chili” ],“price” : 19.99

}}

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JSON Example

{ "type": "document", "students": [ "tom", "sally", "joe" ], "class room": 112, "teach": "Hank McCoy“, “fulltime” : false}

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Dissect the JSON Data{ "type": "document", "students": [ { "name": "tom", "age": 18 }, { "name": "sally", "age": 18 }, { "name": "joe", "age": 17 } ], "class room": 112, "teacher": "Hank McCoy", "fulltime": false}

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Create a JSON Objectvar class = { "type": "document", "students": [ "tom", "sally", "joe" ], "class room": 112, "teach": "Hank McCoy"};

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Navigating a JSON Objectvar json = { "type": "document", "students": [ { "name": "tom", "age": 18 }, { "name": "sally", "age": 18 }, { "name": "joe", "age": 17 } ], "class room": 112, "teacher": "Hank McCoy", "fulltime": false}

JSON Objects are just Javascript Objects,therefore, its easy to access pairs inside the object.

To access a pair, use the pair’s name as an attribute of the object to access the value.

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Navigating a JSON Objectvar json = { "type": "document", "students": [ { "name": "tom", "age": 18 }, { "name": "sally", "age": 18 }, { "name": "joe", "age": 17 } ], "class room": 112, "teacher": "Hank McCoy", "fulltime": false}

json.type; // “document”json.students[0].name; // “tom”json.students[0].age; // 18json.students[1].name; // “sally”json.students.length; // 3json[“class room”]; // 112json.teacher; // “Hank McCoy”json.fulltime; // false

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JSON Methods

• JSON.stringify() to convert object to JSON string

• JSON.parse() to convert JSON string to JS Object.

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JS Object JSON JS Object//Create a javascript Objectvar foo = {};foo.bar = "something";foo.baz = 7;

//Converts JS Object into a JSON stringvar json = JSON.stringify(foo); //"{"bar":"something","baz": 7}“

//Converts JSON string back into JS Objectjson = JSON.parse(json);console.log(json.bar); // “something”console.log(json.baz); // 7

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Your turn

• Use AJAX to fetch the following JSON: http://lyle.smu.edu/~craley/3345/http/drink_genie/supplies.json

• Print out to the console the JSON data for all pairs whose name equals quantity.