JavaScript Mixins

Let's start by defining what a mixin is. I would explain it as a way to share set of data (functions, methods, variables…) with objects.

How does that look like? Let's say we have two functions Clark and Bruce and that we want to implement two methods sayName and secretIdentity to their prototypes.

This is how our functions would look like:

function Clark() {
    this.name = 'Clark Kent';
    this.alterego = 'Superman';
}
Clark.prototype.fly = function () {
    this.fly = true;
};

function Bruce() {
    this.name = 'Bruce Wayne';
    this.alterego = 'Batman';
}
Bruce.prototype.talk = function () {
    return "I'm Batman";
};

Most common ways of adding the methods these functions are:

1. Extending objects

Extending object doesn't really fit our description of mixins, since we are extending instead mixing, though idea is the same. At least that's the way I see it.

var Superhero = {
    sayName: function () {
        return this.name;
    },
    secretIdentity: function () {
        return this.alterego;
    }
};

// Here we extend function prototypes with object using jQuery.extend
$.extend(Clark.prototype, Superhero);
$.extend(Bruce.prototype, Superhero);

Biggest downside to this approach is that you'll either need extend function available from some library like Underscore or jQuery or you would have to write it.

2. Functional mixin

They don't require any additional library and they are faster compared to extending. Also I find this implementation frequently overlooked.

function Superhero () {
    this.sayName = function () {
        return this.name;
    };
    this.secretIdentity = function () {
        return this.alterego;
    };
}

// Here we extend function prototypes with using mixin function
Superhero.call(Clark.prototype);
Superhero.call(Bruce.prototype);

Which approach do you prefer?