Function.prototype.New =
Function.prototype.newInstance = function(){
        for(var i=0,arg=[];i<arguments.length;i++) arg.push("arguments["+i+"]");
        eval("var ins = new this("+arg.join(",")+")");
        return ins;
}

// example

// way to get [1,2,3]
new Array(1,2,3)
Array.New(1,2,3)
Array.newInstance(1,2,3)

// getClass and newInstance
var foo = [];
foo.constructor.New("12345") // [12345]

var foo = "";
foo.constructor.New("12345") // "12345"