kevin whinnery: write better javascript

Write Better JavaScript

Kevin Whinnery

Kevin Whinnery Engineer and Platform Evangelist Appcelerator since 2008

Husband and father of three:

Web developer and JavaScript slinger turned mobile and desktop hacker.

http://kevinwhinnery.com http://twitter.com/kevinwhinnery http://github.com/kwhinnery

Agenda

•  The Good Parts and Bad Parts

•  Object-Oriented Programming in JavaScript

•  Useful JavaScript Patterns, Tricks, and Style Guidelines

•  JavaScript in Titanium Mobile

•  Further Reading

JavaScript is a tragically

misunderstood language.

“JavaScript is the incredibly hot girl at the

party that brings her loser boyfriend DOM”

Tom Robinson Founder, 280 North

JavaScript – What is it good for?

•  Absolutely nothing? Far from it…

•  Object-Oriented (Prototypical Inheritance)… or not

•  Flexible Objects

•  First-Class Functions

•  Built for event-driven UI

JavaScript: The Good Parts

•  Published In 2008 by Doug Crockford

•  Covers the good and bad

•  I use patterns from this book every time I write JS

•  Buy/read/love

Some Bad Parts

Global Variables app.js

some/library.js

Truthy and Falsy

•  Falsy Values: •  false •  0 •  ‘’ •  null •  undefined •  NaN

•  Truthy Values: •  Everything else

•  Almost always, you want === and !==

Floating Point Arithmetic

Avoid this by converting to whole numbers, and converting back to decimal.

typeof is a liar

there’s more (http://wtfjs.com ), but let’s skip to…

The Good Parts

Expressive Object Literals

Easy Object Serialization

First Class Functions

Flexible Objects

Duck Typing

…plus it’s EVERYWHERE. one could develop all kinds of software

applications with nothing else.

OOP! (There it is!)

JavaScript has Prototypal Inheritance, which creates new copies of objects

from an existing object (the prototype)

there’s much more to it than this, but we’ll keep it mostly high level…

Object Constructors

* The capital first letter is by convention, not requirement.

Object Prototype

we could have also wrote…

…but object instantiation using the prototype to define functions/

properties is faster.

http://ejohn.org/blog/simple-class-instantiation mentions this and other methods for…

Inheritance (One Approach)

JavaScript doesn’t support multiple inheritance, but there are multiple

libraries that handle that and more, including underscore.js

http://documentcloud.github.com/underscore/#extend

Parasitic Inheritance

•  Create an existing object

•  Add new features and functionality to it (the parasites, if you will)

•  Pass it off as an instance of a new object

•  Slightly slower than .prototype but more flexible (and inescapable in certain cases)

Parasitic Inheritance

Useful Tricks

Self-Calling Function

•  Function scope is the only scope in JavaScript

•  Self-calling function provides encapsulation

•  Both forms at right are valid, second is preferred

Module Pattern

•  Necessary for <script> in the browser or Ti.include

•  Uses functional scope to provide a public interface to a module

•  Tweetanium/Training demos use a version of this

Dynamic Function Signatures

•  Not necessary to explicitly name parameters

•  Function interfaces can rationalize many input types

•  jQuery does this well, and is very popular b/c of its API

Call And Apply

•  Functions are first class objects

•  Passable, and callable

•  Can replace “this” inside function with something more useful

•  call: call a function with known arguments

•  apply: call a function with an array of arguments

Apply Example

Call Example

A More Useful “this”

Style Guidelines

Style “Dos”

•  Use descriptive variable names (exception: well-understood, frequently typed modules/libraries, like “Ti” or “_” for Underscore.js)

•  JavaScript file contents (cohesion)

•  Google Style Guidelines: http://bit.ly/g_style

•  Follow the above and you are good to go

Style “Don’ts”

•  terse local variable names – excuse me if I don’t know what “tvr” means inside your 300 line constructor

•  Huge files – if you want to write 13,000 lines in a file, go back to enterprise Java

•  Semicolons are not optional – you don’t want the interpreter writing code for you

•  and these monstrosities…

Curly braces on the next line

*this style will actually break in some environments (semicolon insertion)

Unnecessary Indentation

JavaScript in Titanium Mobile

JavaScript Engines

•  iOS – JavaScriptCore – C-based, pretty darn fast

•  Android – Rhino – Java-based, meant for the server-side or desktop, just okay in terms of performance

•  Coming soon – Android/V8 – C-based, super duper fast, minimum Android version 2.2 (don’t freak out, check the version distribution stats)

•  Android: Very important not to load all scripts up front in large applications (slow)

Titanium Features

•  Built-in JSON serialization

•  CommonJS Module Spec

•  Proxy objects are special – what’s a proxy? A stand-in for a native object, like anything you get back from something like:

What’s special about proxies?

•  You can’t modify the prototype

•  You can’t add functions or properties that start with “get” or “set” – these are magic in Titanium proxies:

Further Reading

Books and Reference

•  Mozilla Developer Network JavaScript Reference

•  JavaScript: The Good Parts

•  Eloquent JavaScript (free!)

•  High Performance JavaScript

•  JavaScript Patterns

Not Exhaustive “Must Follow” List

•  @kevinwhinnery J •  @BrendanEich •  @functionsource •  @dalmaer •  @thomasfuchs •  @zacharyjohnson •  @wycats •  @DavidKaneda •  @rem •  @dawsontoth (Titanium goodness)

Potpourri

•  http://javascriptweekly.com - seriously, stop what you’re doing and go there right now

•  http://badassjs.com - then, after that, go here

•  http://jsbin.com - handy test harness

•  https://github.com/cjohansen/juicer - Great compression and obfuscation utility (Ruby)

•  http://crockford.com - Pay your respects

Questions?

Thank You!