support.js

/** Used for native method references. */
var objectProto = Object.prototype;

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

/** Native method references. */
var propertyIsEnumerable = objectProto.propertyIsEnumerable;

/**
 * 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 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 = /\bthis\b/.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 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 the number of function parameters and
   * whose associated argument values are `0`.
   *
   * @memberOf _.support
   * @type boolean
   */
  try {
    support.nonEnumArgs = !propertyIsEnumerable.call(arguments, 1);
  } catch(e) {
    support.nonEnumArgs = true;
  }
}(1, 0));

module.exports = support;