Shortcut to a constructor call

Question

Below, is a simplified version of my App, the following code works as intended. I can see 4 logs in my console with the arguments I passed to SayHello.

var App = {};

(function(that){

    that.SayHello = function(){
        console.log( arguments );
        return {
            doSomething: function(){
                console.log('done');
            }
        };
    };

    var obj = {
        t: new that.SayHello( 'a', 1 ),
        r: new that.SayHello( 'b', 2 ),
        b: new that.SayHello( 'c', 3 ),
        l: new that.SayHello( 'd', 4 )
    };

}(App));

issue: I am trying to create a "shortcut" to new that.SayHello as follow:

var Greet = function(){
        return new that.SayHello;
    },
    obj = {
        t: Greet( 'a', 1 ),
        r: Greet( 'b', 2 ),
        b: Greet( 'c', 3 ),
        l: Greet( 'd', 4 )
    };

The console logs 4 empty arrays. Wich means the arguments failed to pass.

I also tried return new that.SayHello.apply(this, arguments); and return new that.SayHello.call(this, arguments);.

How can I pass ALL Greet's arguments to that.SayHello ?
Knowing that I have to initialize that.SayHello using new that.SayHello or else my code breaks.

I am looking for a general solution for any number of arguments, I don't want to pass the arguments one by one.

This code is also available on jsfiddle.

Answer 1

Something like this?

var Greet = function(){
    var result = that.SayHello.prototype;
    that.SayHello.apply(result, arguments);
    return result;
}

You should know that apply applies arguments to object result. Predefining result as a SayHello prototype will give you what you want.

EDIT

Unfortunetly the code above will alter the prototype of SayHello. This is obviously unwanted behaviour so to avoid this I think we should copy the prototype object. For example use the following code

function clone(obj) {
    if (null == obj || "object" != typeof obj) return obj;
    var copy = obj.constructor();
    for (var attr in obj) {
        if (obj.hasOwnProperty(attr)) copy[attr] = obj[attr];
    }
    return copy;
}

var Greet = function(){
    var result = clone(that.SayHello.prototype);
    that.SayHello.apply(result, arguments);
    return result;
}

I've found this simple version of clone function in this answer. There are many problems with it and you should check other answers. For example using jQuery's $.extend({},originalObject) might be a good idea.

Note that if you don't care about prototype chaining (although you should) you can always do something very simple like this:

var Greet = function(){
    var result = {};
    that.SayHello.apply(result, arguments);
    return result;
}

If you don't care about older browsers (ECMAScript 5) then you can use Object.create method:

var Greet = function(){
    var result = Object.create(that.SayHello.prototype);
    that.SayHello.apply(result, arguments);
    return result;
}