Question

I use the following function to create instances of functions in JavaScript from an array of arguments:

var instantiate = function (instantiate) {
    return function (constructor, args, prototype) {
        "use strict";

        if (prototype) {
            var proto = constructor.prototype;
            constructor.prototype = prototype;
        }

        var instance = instantiate(constructor, args);
        if (proto) constructor.prototype = proto;
        return instance;
    };
}(Function.prototype.apply.bind(function () {
    var args = Array.prototype.slice.call(arguments);
    var constructor = Function.prototype.bind.apply(this, [null].concat(args));
    return new constructor;
}));

Using the above function you can create instances as follows (see the fiddle):

var f = instantiate(F, [], G.prototype);

alert(f instanceof F); // false
alert(f instanceof G); // true

f.alert(); // F

function F() {
    this.alert = function () {
        alert("F");
    };
}

function G() {
    this.alert = function () {
        alert("G");
    };
}

The above code works for user built constructors like F. However it doesn’t work for native constructors like Array for obvious security reasons. You may always create an array and then change its __proto__ property but I am using this code in Rhino so it won’t work there. Is there any other way to achieve the same result in JavaScript?

Answer 1

You can’t fully subclass an array.

However, you can use Object.create to remove a lot of complexity from your current code (ex).