modernizr/src/isEventSupported.js

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

define(['ModernizrProto', 'createElement'], function( ModernizrProto, createElement ) {
  // isEventSupported determines if the given element supports the given event
  // kangax.github.com/iseventsupported/
  // github.com/Modernizr/Modernizr/pull/636
  //
  // Known incorrects:
  //   Modernizr.hasEvent("webkitTransitionEnd", elem) // false negative
  //   Modernizr.hasEvent("textInput") // in Webkit. github.com/Modernizr/Modernizr/issues/333
  var isEventSupported = (function (undefined) {

    // 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);

    /**
     * @param  {string|*}           eventName  is the name of an event to test for (e.g. "resize")
     * @param  {(Object|string|*)=} element    is the element|document|window|tagName to test on
     * @return {boolean}
     */
    function isEventSupportedInner( 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');
        }
        if ( element.setAttribute && element.removeAttribute ) {
          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 isEventSupportedInner;
  })();

  return isEventSupported;
});