modernizr/src/hasEvent.js

Modernizr is a JavaScript library that detects HTML5 and CSS3 features in the user’s browser.

define(['ModernizrProto', 'createElement'], function(ModernizrProto, createElement) {
  /**
   * Modernizr.hasEvent() detects support for a given event
   *
   * @memberof Modernizr
   * @name Modernizr.hasEvent
   * @optionName Modernizr.hasEvent()
   * @optionProp hasEvent
   * @access public
   * @function hasEvent
   * @param  {string|*} eventName - the name of an event to test for (e.g. "resize")
   * @param  {Element|string} [element=HTMLDivElement] - is the element|document|window|tagName to test on
   * @returns {boolean}
   * @example
   *  `Modernizr.hasEvent` lets you determine if the browser supports a supplied event.
   *  By default, it does this detection on a div element
   *
   * ```js
   *  hasEvent('blur') // true;
   * ```
   *
   * However, you are able to give an object as a second argument to hasEvent to
   * detect an event on something other than a div.
   *
   * ```js
   *  hasEvent('devicelight', window) // true;
   * ```
   *
   */

  var hasEvent = (function() {

    // Detect whether event support can be detected via `in`. Test on a DOM element
    // using the "blur" event b/c it should always exist. bit.ly/event-detection
    var needsFallback = !('onblur' in document.documentElement);

    function inner(eventName, element) {

      var isSupported;
      if (!eventName) { return false; }
      if (!element || typeof element === 'string') {
        element = createElement(element || 'div');
      }

      // Testing via the `in` operator is sufficient for modern browsers and IE.
      // When using `setAttribute`, IE skips "unload", WebKit skips "unload" and
      // "resize", whereas `in` "catches" those.
      eventName = 'on' + eventName;
      isSupported = eventName in element;

      // Fallback technique for old Firefox - bit.ly/event-detection
      if (!isSupported && needsFallback) {
        if (!element.setAttribute) {
          // Switch to generic element if it lacks `setAttribute`.
          // It could be the `document`, `window`, or something else.
          element = createElement('div');
        }

        element.setAttribute(eventName, '');
        isSupported = typeof element[eventName] === 'function';

        if (element[eventName] !== undefined) {
          // If property was created, "remove it" by setting value to `undefined`.
          element[eventName] = undefined;
        }
        element.removeAttribute(eventName);
      }

      return isSupported;
    }
    return inner;
  })();


  ModernizrProto.hasEvent = hasEvent;
  return hasEvent;
});