lodash-compat/support.js

The compatibility build of lodash modular utilities.

/** Used for native method references. */
var arrayProto = Array.prototype,
    errorProto = Error.prototype,
    objectProto = Object.prototype;

/** Native method references. */
var propertyIsEnumerable = objectProto.propertyIsEnumerable,
    splice = arrayProto.splice;

/**
 * An object environment feature flags.
 *
 * @static
 * @memberOf _
 * @type Object
 */
var support = {};

(function(x) {
  var Ctor = function() { this.x = x; },
      object = { '0': x, 'length': x },
      props = [];

  Ctor.prototype = { 'valueOf': x, 'y': x };
  for (var key in new Ctor) { props.push(key); }

  /**
   * Detect if `name` or `message` properties of `Error.prototype` are
   * enumerable by default (IE < 9, Safari < 5.1).
   *
   * @memberOf _.support
   * @type boolean
   */
  support.enumErrorProps = propertyIsEnumerable.call(errorProto, 'message') ||
    propertyIsEnumerable.call(errorProto, 'name');

  /**
   * Detect if `prototype` properties are enumerable by default.
   *
   * Firefox < 3.6, Opera > 9.50 - Opera < 11.60, and Safari < 5.1
   * (if the prototype or a property on the prototype has been set)
   * incorrectly set the `[[Enumerable]]` value of a function's `prototype`
   * property to `true`.
   *
   * @memberOf _.support
   * @type boolean
   */
  support.enumPrototypes = propertyIsEnumerable.call(Ctor, 'prototype');

  /**
   * Detect if properties shadowing those on `Object.prototype` are non-enumerable.
   *
   * In IE < 9 an object's own properties, shadowing non-enumerable ones,
   * are made non-enumerable as well (a.k.a the JScript `[[DontEnum]]` bug).
   *
   * @memberOf _.support
   * @type boolean
   */
  support.nonEnumShadows = !/valueOf/.test(props);

  /**
   * Detect if own properties are iterated after inherited properties (IE < 9).
   *
   * @memberOf _.support
   * @type boolean
   */
  support.ownLast = props[0] != 'x';

  /**
   * Detect if `Array#shift` and `Array#splice` augment array-like objects
   * correctly.
   *
   * Firefox < 10, compatibility modes of IE 8, and IE < 9 have buggy Array
   * `shift()` and `splice()` functions that fail to remove the last element,
   * `value[0]`, of array-like objects even though the "length" property is
   * set to `0`. The `shift()` method is buggy in compatibility modes of IE 8,
   * while `splice()` is buggy regardless of mode in IE < 9.
   *
   * @memberOf _.support
   * @type boolean
   */
  support.spliceObjects = (splice.call(object, 0, 1), !object[0]);

  /**
   * Detect lack of support for accessing string characters by index.
   *
   * IE < 8 can't access characters by index. IE 8 can only access characters
   * by index on string literals, not string objects.
   *
   * @memberOf _.support
   * @type boolean
   */
  support.unindexedChars = ('x'[0] + Object('x')[0]) != 'xx';
}(1, 0));

module.exports = support;