ampersand-class-extend.js

var assign = require('lodash/assign');

/// Following code is largely pasted from Backbone.js

// Helper function to correctly set up the prototype chain, for subclasses.
// Similar to `goog.inherits`, but uses a hash of prototype properties and
// class properties to be extended.
var extend = function(protoProps) {
    var parent = this;
    var child;
    var args = [].slice.call(arguments);

    // The constructor function for the new subclass is either defined by you
    // (the "constructor" property in your `extend` definition), or defaulted
    // by us to simply call the parent's constructor.
    if (protoProps && protoProps.hasOwnProperty('constructor')) {
        child = protoProps.constructor;
    } else {
        child = function () {
            return parent.apply(this, arguments);
        };
    }

    // Add static properties to the constructor function from parent
    assign(child, parent);

    // Set the prototype chain to inherit from `parent`, without calling
    // `parent`'s constructor function.
    var Surrogate = function(){ this.constructor = child; };
    Surrogate.prototype = parent.prototype;
    child.prototype = new Surrogate();

    // Mix in all prototype properties to the subclass if supplied.
    if (protoProps) {
        args.unshift(child.prototype);
        assign.apply(null, args);
    }

    // Set a convenience property in case the parent's prototype is needed
    // later.
    child.__super__ = parent.prototype;

    return child;
};

// Expose the extend function
module.exports = extend;