extend.js

/*
 * Backbone's extend functionality, which is almost identical to CoffeeScript's
 * method. This will make it easy to extend classes originally created in
 * CoffeeScript.
 *
 * From: https://github.com/jashkenas/backbone/blob/c33dcdeffd85a5b749100249b8b9de7be44a0594/backbone.js#L1648
 */
'use strict';

var _ = require('underscore');

var extend = function(protoProps, staticProps) {
  var parent = this;
  var child;

  // 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 && _.has(protoProps, 'constructor')) {
    child = protoProps.constructor;
  } else {
    child = function(){ return parent.apply(this, arguments); };
  }

  // Add static properties to the constructor function, if supplied.
  _.extend(child, parent, staticProps);

  // 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();

  // Add prototype properties (instance properties) to the subclass,
  // if supplied.
  if (protoProps) _.extend(child.prototype, protoProps);

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

  return child;
};

module.exports = extend;