Use of .apply() with 'new' operator. Is this possible?

Question

In JavaScript, I want to create an object instance (via the new operator), but pass an arbitrary number of arguments to the constructor. Is this possible?

Answer 1

Here's a generalized solution that can call any constructor (except native constructors that behave differently when called as functions, like String, Number, Date, etc.) with an array of arguments:

function construct(constructor, args) {
    function F() {
        return constructor.apply(this, args);
    }
    F.prototype = constructor.prototype;
    return new F();
}

An object created by calling construct(Class, [1, 2, 3]) would be identical to an object created with new Class(1, 2, 3).

You could also make a more specific version so you don't have to pass the constructor every time. This is also slightly more efficient, since it doesn't need to create a new instance of the inner function every time you call it.

var createSomething = (function() {
    function F(args) {
        return Something.apply(this, args);
    }
    F.prototype = Something.prototype;

    return function(args) {
        return new F(args);
    }
})();

The reason for creating and calling the outer anonymous function like that is to keep function F from polluting the global namespace. It's sometimes called the module pattern.

[UPDATE]

For those who want to use this in TypeScript, since TS gives an error if F returns anything:

function construct(constructor, args) {
    function F() : void {
        constructor.apply(this, args);
    }
    F.prototype = constructor.prototype;
    return new F();
}