Kevin Whinnery: Write Better JavaScript

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One of the main reasons Titanium Mobile has been so successful is that the technology has significantly lowered the barrier to entry for native mobile development. A major force behind this is JavaScript, Titanium's primary programming language. The JavaScript programming language is small enough where the basics can be learned in a matter of hours, which has enabled developers from many different backgrounds to become productive using Titanium. But there's much more to JavaScript than just control structures and a handful of primitive data types - JavaScript is a beautiful functional programming language with great features you might not be using.

Most developers working on the web today have had some exposure to JavaScript, but there's a difference between using jQuery for DOM manipulation on a web page and writing an entire application in JavaScript. This talk, intended for beginner or intermediate JavaScript developers, will focus on the essential language features you will need to write professional JavaScript applications, including but not limited to:

Object Oriented Programming in JavaScript
The Good Parts and Bad Parts of JavaScript
Useful JavaScript Patterns, Tricks, and Style Guidelines
The JavaScript runtime in Titanium Mobile
Further Reading and ways to stay up to date on JavaScript

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Kevin Whinnery: Write Better JavaScript

  1. 1. Write Better JavaScript Kevin Whinnery
  2. 2. Kevin WhinneryEngineer and Platform EvangelistAppcelerator since 2008Husband and father of three:Web developer and JavaScript slingerturned mobile and desktop hacker.http://kevinwhinnery.comhttp://twitter.com/kevinwhinneryhttp://github.com/kwhinnery
  3. 3. 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
  4. 4. JavaScript is a tragicallymisunderstood language.
  5. 5. “JavaScript is the incredibly hot girl at theparty that brings her loser boyfriend DOM” Tom Robinson Founder, 280 North
  6. 6. 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
  7. 7. 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
  8. 8. Some Bad Parts
  9. 9. Global Variablesapp.js some/library.js
  10. 10. Truthy and Falsy•  Falsy Values: •  false •  0 •  ‘’ •  null •  undefined •  NaN•  Truthy Values: •  Everything else•  Almost always, you want === and !==
  11. 11. Floating Point Arithmetic Avoid this by converting to whole numbers, and converting back to decimal.
  12. 12. typeof is a liar
  13. 13. there’s more (http://wtfjs.com ), but let’s skip to…
  14. 14. The Good Parts
  15. 15. Expressive Object Literals
  16. 16. Easy Object Serialization
  17. 17. First Class Functions
  18. 18. Flexible Objects
  19. 19. Duck Typing
  20. 20. …plus it’s EVERYWHERE.one could develop all kinds of software applications with nothing else.
  21. 21. OOP!(There it is!)
  22. 22. JavaScript has Prototypal Inheritance, which creates new copies of objectsfrom an existing object (the prototype) there’s much more to it than this, but we’ll keep it mostly high level…
  23. 23. Object Constructors * The capital first letter is by convention, not requirement.
  24. 24. Object Prototype
  25. 25. we could have also wrote…
  26. 26. …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…
  27. 27. Inheritance (One Approach)
  28. 28. JavaScript doesn’t support multiple inheritance, but there are multiplelibraries that handle that and more, including underscore.js http://documentcloud.github.com/underscore/#extend
  29. 29. 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)
  30. 30. Parasitic Inheritance
  31. 31. Useful Tricks
  32. 32. 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
  33. 33. 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
  34. 34. 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
  35. 35. 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
  36. 36. Apply Example
  37. 37. Call Example
  38. 38. A More Useful “this”
  39. 39. Style Guidelines
  40. 40. 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
  41. 41. 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…
  42. 42. Curly braces on the next line*this style will actually break in some environments (semicolon insertion)
  43. 43. Unnecessary Indentation
  44. 44. JavaScript inTitanium Mobile
  45. 45. 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)
  46. 46. 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:
  47. 47. 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:
  48. 48. Further Reading
  49. 49. Books and Reference•  Mozilla Developer Network JavaScript Reference•  JavaScript: The Good Parts•  Eloquent JavaScript (free!)•  High Performance JavaScript•  JavaScript Patterns
  50. 50. Not Exhaustive “Must Follow” List•  @kevinwhinnery J•  @BrendanEich•  @functionsource•  @dalmaer•  @thomasfuchs•  @zacharyjohnson•  @wycats•  @DavidKaneda•  @rem•  @dawsontoth (Titanium goodness)
  51. 51. 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
  52. 52. Questions?
  53. 53. Thank You!

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