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for (var name in prop) {
// Check if we're overwriting an existing function
prototype[name] = typeof prop[name] == "function" &&
typeof _super[name] == "function" &&
fnTest.test(prop[name]) ?
(function(name, fn){
return function() {
var tmp = this._super;
// Add a new ._super() method that is the same method
// but on the super-class
this._super = _super[name];
// The method only need to be bound temporarily, so we
// remove it when we're done executing
var ret = fn.apply(this, arguments);
this._super = tmp;
return ret;
})(name, prop[name]) :
// The dummy class constructor
function Class() {
// All construction is actually done in the init method
if ( !initializing && this.init )
this.init.apply(this, arguments);
// Populate our constructed prototype object
Class.prototype = prototype;
// Enforce the constructor to be what we expect
Class.prototype.constructor = Class;
// And make this class extendable
Class.extend = arguments.callee;
return Class;
The main gist of this code is to allow new classes to be extended from existing ones using the extend
method. Inherited objects can share the same instance methods as the parent objects and call parent methods
using this._super() from the child method. This special case is handled by the loop in the middle, which,
instead of just copying the entire method over blindly, checks for an existing method on the parent and then
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