关于object.extend在prototype和google doctype里的对比-优快云博客

本文对比分析了prototype.js和googledoctype中实现的Object.extend方法，详细解析了如何通过该方法扩展对象，特别是在处理Object.prototype中定义的方法时的区别。

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prototype.js里的代码：

Object.extend = function(destination, source) {
  for (var property in source)
    destination[property] = source[property];
  return destination;
};

google doctype里的代码：

/**
 * The names of the fields that are defined on Object.prototype.
 * @type {Array.<string>}
 * @private
 */
goog.object.PROTOTYPE_FIELDS_ = [
  'constructor',
  'hasOwnProperty',
  'isPrototypeOf',
  'propertyIsEnumerable',
  'toLocaleString',
  'toString',
  'valueOf'
];


/**
 * Extends an object with another object.
 * This operates 'in-place'; it does not create a new Object.
 *
 * Example:
 * var o = {};
 * goog.object.extend(o, {a: 0, b: 1});
 * o; // {a: 0, b: 1}
 * goog.object.extend(o, {c: 2});
 * o; // {a: 0, b: 1, c: 2}
 *
 * @param {Object} target  The object to modify.
 * @param {Object} var_args The objects from which values will be copied.
 */
goog.object.extend = function(target, var_args) {
  var key, source;
  for (var i = 1; i < arguments.length; i++) {
    source = arguments[i];
    for (key in source) {
      target[key] = source[key];
    }

    // For IE the for-in-loop does not contain any properties that are not
    // enumerable on the prototype object (for example isPrototypeOf from
    // Object.prototype) and it will also not include 'replace' on objects that
    // extend String and change 'replace' (not that it is common for anyone to
    // extend anything except Object).

    for (var j = 0; j < goog.object.PROTOTYPE_FIELDS_.length; j++) {
      key = goog.object.PROTOTYPE_FIELDS_[j];
      if (Object.prototype.hasOwnProperty.call(source, key)) {
        target[key] = source[key];
      }
    }
  }
};

可以看出，google doctype多考虑了object的某些属性、方法，确保它们能够真正地被“extend”到新对象里。

参看资料：

http://code.google.com/doctype/