support.js

define(['./lang/isNative', './internal/root'], function(isNative, root) {

  /** `Object#toString` result references. */
  var argsTag = '[object Arguments]',
      objectTag = '[object Object]';

  /** Used to detect functions containing a `this` reference. */
  var reThis = /\bthis\b/;

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

  /** Used to detect DOM support. */
  var document = (document = root.window) && document.document;

  /**
   * Used to resolve the `toStringTag` of values.
   * See the [ES spec](https://people.mozilla.org/~jorendorff/es6-draft.html#sec-object.prototype.tostring)
   * for more details.
   */
  var objToString = objectProto.toString;

  /** 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 = 1; },
        object = { '0': 1, 'length': 1 },
        props = [];

    Ctor.prototype = { 'valueOf': 1, 'y': 1 };
    for (var key in new Ctor) { props.push(key); }

    /**
     * Detect if the `toStringTag` of `arguments` objects is resolvable
     * (all but Firefox < 4, IE < 9).
     *
     * @memberOf _.support
     * @type boolean
     */
    support.argsTag = objToString.call(arguments) == argsTag;

    /**
     * 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 functions can be decompiled by `Function#toString`
     * (all but Firefox OS certified apps, older Opera mobile browsers, and
     * the PlayStation 3; forced `false` for Windows 8 apps).
     *
     * @memberOf _.support
     * @type boolean
     */
    support.funcDecomp = !isNative(root.WinRTError) && reThis.test(function() { return this; });

    /**
     * Detect if `Function#name` is supported (all but IE).
     *
     * @memberOf _.support
     * @type boolean
     */
    support.funcNames = typeof Function.name == 'string';

    /**
     * Detect if the `toStringTag` of DOM nodes is resolvable (all but IE < 9).
     *
     * @memberOf _.support
     * @type boolean
     */
    support.nodeTag = objToString.call(document) != objectTag;

    /**
     * Detect if string indexes are non-enumerable
     * (IE < 9, RingoJS, Rhino, Narwhal).
     *
     * @memberOf _.support
     * @type boolean
     */
    support.nonEnumStrings = !propertyIsEnumerable.call('x', 0);

    /**
     * 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';

    /**
     * Detect if the DOM is supported.
     *
     * @memberOf _.support
     * @type boolean
     */
    try {
      support.dom = document.createDocumentFragment().nodeType === 11;
    } catch(e) {
      support.dom = false;
    }

    /**
     * Detect if `arguments` object indexes are non-enumerable.
     *
     * In Firefox < 4, IE < 9, PhantomJS, and Safari < 5.1 `arguments` object
     * indexes are non-enumerable. Chrome < 25 and Node.js < 0.11.0 treat
     * `arguments` object indexes as non-enumerable and fail `hasOwnProperty`
     * checks for indexes that exceed their function's formal parameters with
     * associated values of `0`.
     *
     * @memberOf _.support
     * @type boolean
     */
    try {
      support.nonEnumArgs = !propertyIsEnumerable.call(arguments, 1);
    } catch(e) {
      support.nonEnumArgs = true;
    }
  }(0, 0));

  return support;
});