Mixins in JavaScript - a simple way

As in my previous protip, I'm going to introduce the 'ex' helper function first:

function ex (destination, source) {
  var p;

  for (p in source) {
    if (source.hasOwnProperty(p)) {
      destination[p] = source[p];
    }
  }
  return destination;
}

Nothing special, just copies the source's properties into the destination.

And here is our mixin function:

function mixin () {
    var i, ln = arguments.length;
    for (i = 0; i < ln; i++) {
        ex(this.prototype, arguments[i]);
    }
};

Again nothing special - it takes 0+ mixin objects and using the helper 'ex' function adds their properties to the current context object.

Here is an example:

function Foo (a, b) {
    this.a = a;
    this.b = b;
}

Foo.include = mixin;

Foo.prototype = {
    constructor: Foo,
    c: function () {
        return this.a + this.b;
    }
};

This is our class foo, it can handle mixins (see how we assigned the 'mixin' function to be its 'include' method).

And let's mix some object in Foo:

Foo.include({
    d: 5,
    e: function () {
        return this.d * this.d;
    }
});

Here we go:

var foo = new Foo(1, 2);

console.log(foo.c()); // 3
console.log(foo.e()); // 25

console.log(foo.constructor.prototype); 

Try it here