Inheritance Discussion

crockford-quote.md

I have been writing JavaScript for 14 years now, and I have never once found need to use an uber function. The super idea is fairly important in the classical pattern, but it appears to be unnecessary in the prototypal and functional patterns. I now see my early attempts to support the classical model in JavaScript as a mistake. [Ed.: Emphasis Added]

~ Douglas Crockford, in addendum to Classical Inheritance in JavaScript

es5-extend.js

// From Node.js older version :
// https://github.com/nodejs/node/blob/8b4adb267b9320c78e1508b1c973efd256e15b21/lib/util.js#L764-L771

/**
 * Inherit the prototype methods from one constructor into another.
 *
 * The Function.prototype.inherits from lang.js rewritten as a standalone
 * function (not on Function.prototype). NOTE: If this file is to be loaded
 * during bootstrapping this function needs to be rewritten using some native
 * functions as prototype setup using normal JavaScript does not work as
 * expected during bootstrapping (see mirror.js in r114903).
 *
 * @param {function} ctor Constructor function which needs to inherit the
 *     prototype.
 * @param {function} superCtor Constructor function to inherit prototype from.
 * @throws {TypeError} Will error if either constructor is null, or if
 *     the super constructor lacks a prototype.
 */
exports.inherits = function(ctor, superCtor) {

  if (ctor === undefined || ctor === null)
    throw new TypeError('The constructor to `inherits` must not be ' +
                        'null or undefined.');

  if (superCtor === undefined || superCtor === null)
    throw new TypeError('The super constructor to `inherits` must not ' +
                        'be null or undefined.');

  if (superCtor.prototype === undefined)
    throw new TypeError('The super constructor to `inherits` must ' +
                        'have a prototype.');

  ctor.super_ = superCtor;
  ctor.prototype = Object.create(superCtor.prototype, {
    constructor: {
      value: ctor,
      enumerable: false,
      writable: true,
      configurable: true
    }
  });
};

exports._extend = function(origin, add) {
  // Don't do anything if add isn't an object
  if (add === null || typeof add !== 'object') return origin;

  var keys = Object.keys(add);
  var i = keys.length;
  while (i--) {
    origin[keys[i]] = add[keys[i]];
  }
  return origin;
};

function hasOwnProperty(obj, prop) {
  return Object.prototype.hasOwnProperty.call(obj, prop);
}

es6-extend.js

// From Node.js latest :
// https://github.com/nodejs/node/blob/6526ae7b37316e301ff12accd2671640ae4a48c1/lib/util.js#L775-L822

/**
 * Inherit the prototype methods from one constructor into another.
 *
 * The Function.prototype.inherits from lang.js rewritten as a standalone
 * function (not on Function.prototype). NOTE: If this file is to be loaded
 * during bootstrapping this function needs to be rewritten using some native
 * functions as prototype setup using normal JavaScript does not work as
 * expected during bootstrapping (see mirror.js in r114903).
 *
 * @param {function} ctor Constructor function which needs to inherit the
 *     prototype.
 * @param {function} superCtor Constructor function to inherit prototype from.
 * @throws {TypeError} Will error if either constructor is null, or if
 *     the super constructor lacks a prototype.
 */
exports.inherits = function(ctor, superCtor) {

  if (ctor === undefined || ctor === null)
    throw new TypeError('The constructor to "inherits" must not be ' +
                        'null or undefined');

  if (superCtor === undefined || superCtor === null)
    throw new TypeError('The super constructor to "inherits" must not ' +
                        'be null or undefined');

  if (superCtor.prototype === undefined)
    throw new TypeError('The super constructor to "inherits" must ' +
                        'have a prototype');

  ctor.super_ = superCtor;
  Object.setPrototypeOf(ctor.prototype, superCtor.prototype);
};

exports._extend = function(origin, add) {
  // Don't do anything if add isn't an object
  if (add === null || typeof add !== 'object') return origin;

  var keys = Object.keys(add);
  var i = keys.length;
  while (i--) {
    origin[keys[i]] = add[keys[i]];
  }
  return origin;
};

function hasOwnProperty(obj, prop) {
  return Object.prototype.hasOwnProperty.call(obj, prop);
}