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Metaprogramming, writing code that augments itself at runtime, is a very powerful technique gaining popularity in scripting languages like Python and Ruby but surely little old JavaScript isn't flexible enough to do this? Think again. In this presentation, we'll deconstruct the features of JavaScript that allow metaprogramming then move on to combining these to produce elegant solutions to real world tasks. In the process, we'll take an in-depth look at closures, functional programming, prototype inheritance and more. Bring your best brain, you'll need it.
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What?
the writing of computer programs that write or manipulate other programs (or themselves) as theirdata”“
”
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
JavaScript Exposed:Objects Out Of
Control!
Play along!
4 building blocks
(Nearly) everything is a hash
numberstring
booleanundefined
everything else is an Object
This works with any object
Expandos: a special case
Inspecting objects
Inspecting types
Wha?!
First typeofthen instanceof
Functions are Objects
'Methods' are just functions that are
assigned to a property of an object
arguments
Functions can return other functions
Closure
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. “ ”
Why is that useful?
Functions can be used to make objects
Constructor functionsare just functions
The magic is inthe new operator
inheritance
The point is:its all just functions,
objects and properties
We can hack it all.
So what can you do with this stuff?
Patch holes in bad implementations
Self optimising code
Pretty APIs
Domain Specific Languages
DIY language features
John Resig's method overloading
http://ejohn.org/blog/javascript-method-overloading/
Prototype 1.6 Classeshttp://prototypejs.org/learn/class-inheritance
and a lot more...
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.
Coming Soon...
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