Metaprogramming JavaScript

Slide 1: Metaprogramming JavaScript Dan Webb (dan@danwebb.net)

Slide 2: What? “ the writing of computer programs that write or manipulate other programs (or themselves) as their data”

Slide 3: With JavaScript?! ★ Small and fiesty but widely misunderstood ★ Relies on few but powerful constructs ★ You can work with functions, arguments, built-ins types and mechanisms like inheritance at runtime ★ Techniques underpin many JS libraries

Slide 4: JavaScript Exposed: Objects Out Of Control!

Slide 5: Play along!

Slide 6: 4 building blocks

Slide 7: (Nearly) everything is a hash

Slide 8: number string boolean undefined

Slide 9: everything else is an Object

Slide 11: This works with any object

Slide 13: Expandos: a special case

Slide 17: Inspecting objects

Slide 20: Inspecting types

Slide 24: Wha?!

Slide 26: First typeof then instanceof

Slide 27: Functions are Objects

Slide 29: 'Methods' are just functions that are assigned to a property of an object

Slide 38: arguments

Slide 42: Functions can return other functions

Slide 45: Closure

Slide 46: Back to wikipedia... “ A closure occurs when a function is defined within another function, and the inner function refers to local variables of the outer function.

Slide 49: Why is that useful?

Slide 53: Functions can be used to make objects

Slide 55: Constructor functions are just functions

Slide 56: The magic is in the new operator

Slide 60: inheritance

Slide 67: The point is: its all just functions, objects and properties

Slide 68: We can hack it all.

Slide 69: So what can you do with this stuff?

Slide 70: Patch holes in bad implementations

Slide 73: Self optimising code

Slide 76: Pretty APIs

Slide 79: Domain Specific Languages

Slide 80: DOMBuilder http://danwebb.net/lowpro

Slide 84: DIY language features

Slide 85: John Resig's method overloading http://ejohn.org/blog/javascript-method-overloading/

Slide 89: Prototype 1.6 Classes http://prototypejs.org/learn/class-inheritance

Slide 92: and a lot more...

Slide 93: Looking back... ★ JavaScript is small but totally flexible ★ A handful of techniques provide everything you need ★ It's all about objects, properties and functions ★ Don't worry if its not all sunk in. Have a play around. Slides will be available.

Slide 94: Coming Soon...