how to implement this._super in js function

gistfile1

// tests if we can get super in .toString()
fnTest = /xyz/.test(function() {
	xyz;
}) ? /\b_super\b/ : /.*/,
		
// overwrites an object with methods, sets up _super
//   newProps - new properties
//   oldProps - where the old properties might be
//   addTo - what we are adding to
inheritProps = function( newProps, oldProps, addTo ) {
	addTo = addTo || newProps
	for ( var name in newProps ) {
		// Check if we're overwriting an existing function
		addTo[name] = isFunction(newProps[name]) && 
			isFunction(oldProps[name]) && 
			fnTest.test(newProps[name]) ? (function( name, fn ) {
				return function() {
					var tmp = this._super,
						ret;

					// Add a new ._super() method that is the same method
					// but on the super-class
					this._super = oldProps[name];

					// The method only need to be bound temporarily, so we
					// remove it when we're done executing
					ret = fn.apply(this, arguments);
					this._super = tmp;
					return ret;
					};
			})(name, newProps[name]) : newProps[name];
	}
}

1.fnTest 测试 Function.toString 方法是否被覆写，未被覆写的情况下，输出function的源代码。
2.fnTest.test(newProps[name])判断function中是否有this._super调用，如果有着代理该方法，将this._super赋给该方法的父类方法。
3.var tmp = this._super 缓存this._super若子类中定义了this._super，不会生效，以为所有调用this._super的地方都被代理了。this._super = tmp;的作用基本上就是还原this._super的undefined值而已。