binding/applying constructors in JavaScript

Question

I was looking for solutions for calling Javascript constructors with an arbitrary number of arguments, and found some good SO posts, which led me to believe that these three

Answer 1

bind and apply / call only works work invocation to function but not constructor, so basically with native methods you cannot do this, one way is to write a bindConstruct method but it may involves extra complexity:

function bindConstruct(fn) {
    // since constructor always accepts a static this value
    // so bindConstruct cannot specify this
    var extraArgs = [].slice.call(arguments, 1);

    // create a 'subclass' of fn
    function sub() {
        var args = extraArgs.concat([].slice.call(arguments));
        fn.apply(this, args);
    }
    sub.prototype = fn.prototype;
    sub.prototype.constructor = sub;

    return sub;
}

This, actually, creates a subclass to your constructor.

Then your code:

var MyClass = function(x, y) {
    console.log(arguments);
    console.log(x + y);
}
var BindedMyClass = bindConstruct(MyClass, 1, 2, 3);
var c = new BindedMyClass(4, 5);
console.log(c instanceof MyClass);
console.log(c instanceof BindedMyClass);

You may also write this function to Function.prototype or as an extension to the native bind function.