Mixin in typescript

TypeScript Mixin

//Addapted from this page http://lostechies.com/derickbailey/2012/10/07/javascript-mixins-beyond-simple-object-extension/

module Mixer {
    // build a mixin function to take a target that receives the mixin, 
    // a source that is the mixin, and a list of methods / attributes to
    // copy over to the target
    export function mix(target, source, methodNames){
 
        // ignore the actual args list and build from arguments so we can
        // be sure to get all of the method names
        var args = Array.prototype.slice.apply(arguments);
        target = args.shift();
        source = args.shift();
        methodNames = args.shift();
 
        var method;
        var length = methodNames.length;
        for(var i = 0; i < length; i++){
            method = methodNames[i];
 
            // build a function with a closure around the source
            // and forward the method call to the source, passing
            // along the method parameters and setting the context
            target[method] = function(){
                var args = Array.prototype.slice.apply(arguments);
                source[method].apply(source, args);
            }
        }
    }
}

var $mx = Mixer;  

module MixerTests {
    export class NameOnly {
        public name: string;
    }

    export class MultiMember {
        name: string; 
        copyMe1: string;
        copyMe2: string; 
        dontCopy1: string; 
        dontCopy2: string; 
    }

    export function run() {
        var target = new NameOnly();
        target.name = "target"; 

        var source = new MultiMember();
        source.name = "source";
        source.copyMe1 = "c1"; 
        source.copyMe2 = "c2";
        source.dontCopy1 = "d1";
        source.dontCopy2 = "d2"; 
        
        isMixinAndOnlyMixinApplied(target, source, ['copyMe1', 'copyMe2']); 
    }

    export function isMixinAndOnlyMixinApplied(target, source, methodNames) {
        var index = methodNames.length - 1,
            sourceProps = Object.getOwnPropertyNames(source),
            targetProps = Object.getOwnPropertyNames(target),
            method; 


        $mx.mix(target, source, methodNames); 
        //Check to see that mix methods exist.
        do {
            method = methodNames[index];
            Assert.isTrue(target[method], method + ' exists'); 
        } while (index--); 

        index = sourceProps.length - 1;
        method = '';

        //Check to see if non-mixed methods exist.
        do {
            method = sourceProps[index]; 
            if(methodNames.indexOf(method) !== -1 || targetProps.indexOf(method) !== -1)
                continue;

            Assert.isFalse(target[method], method + " does not exist as expected.");
        } while (index--); 

        Assert.isTrue((<MultiMember>target).copyMe1 && true, "Type casting passes compiler check with intellisense."); 
    }

}
$(function () {
    MixerTests.run();
});