object-foreach.js

// Based on work by John-David Dalton, Juriy Zaytsev, and Asen Bozhilov.
Object.forEach = (function () {
  // Convenience aliases.
  var toString = {}.toString, hasOwnProperty = {}.hasOwnProperty ||
    // Simulate `Object#hasOwnProperty` in Safari 2.
    function (property) {
      // Save the original prototype chain.
      var original = this.__proto__, result;
      // Break the prototype chain.
      this.__proto__ = null;
      result = property in this;
      // Restore the prototype chain.
      this.__proto__ = original;
      return result;
  }, forEach;

  // The `Properties` constructor tests for bugs in the `for...in` algorithm.
  function Properties() {
    this.toString = 1;
  }
  Properties.prototype.toString = 1;

  // Create and iterate over a new instance of the `Properties` constructor.
  var properties = new Properties, property, length = 0;
  for (property in properties) {
    if (hasOwnProperty.call(properties, property)) {
      length++;
    }
  }

  if (!length) {
    // JScript ignores shadowed non-enumerable properties.
    properties = ['constructor', 'toString', 'valueOf', 'isPrototypeOf',
      'hasOwnProperty', 'propertyIsEnumerable', 'toLocaleString'];
    forEach = function forEach(object, iterator, context) {
      var index = 0, property;
      for (property in object) {
        if (hasOwnProperty.call(object, property) && iterator.call(context,
        object[property], property, object) === false) {
          break;
        }
      }
      // Provide a workaround for the JScript bug.
      while ((property = properties[index++])) {
        if (hasOwnProperty.call(object, property) && iterator.call(context,
        object[property], property, object) === false) {
          break;
        }
      }
    };
  } else if (length == 2) {
    // Safari 2 enumerates all shadowed and inherited properties.
    forEach = function forEach(object, iterator, context) {
      // The `prototype` property is handled inconsistently across browsers.
      var isFunction = toString.call(object) == '[object Function]',
      // Create a cache of iterated properties.
      properties = {}, property;
      for (property in object) {
        // Skip the `prototype` property of functions.
        if (!(isFunction && property == 'prototype') && !hasOwnProperty.call(
        // Cache each property to prevent enumeration of inherited and shadowed
        // properties.
        properties, property) && (properties[property] = 1) &&
        hasOwnProperty.call(object, property) && iterator.call(context,
        object[property], property, object) === false) {
          break;
        }
      }
    };
  } else {
    forEach = function forEach(object, iterator, context) {
      var isFunction = toString.call(object) == '[object Function]', property;
      for (property in object) {
        if (!(isFunction && property == 'prototype') && hasOwnProperty.call(
        object, property) && iterator.call(context, object[property], property,
        object) === false) {
          break;
        }
      }
    };
  }
  return forEach;
})();