isEventSupported.js

/**
 * Copyright 2013-2014, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule isEventSupported
 */

"use strict";

var ExecutionEnvironment = require('ExecutionEnvironment');

var useHasFeature;
if (ExecutionEnvironment.canUseDOM) {
  useHasFeature =
    document.implementation &&
    document.implementation.hasFeature &&
    // always returns true in newer browsers as per the standard.
    // @see http://dom.spec.whatwg.org/#dom-domimplementation-hasfeature
    document.implementation.hasFeature('', '') !== true;
}

/**
 * Checks if an event is supported in the current execution environment.
 *
 * NOTE: This will not work correctly for non-generic events such as `change`,
 * `reset`, `load`, `error`, and `select`.
 *
 * Borrows from Modernizr.
 *
 * @param {string} eventNameSuffix Event name, e.g. "click".
 * @param {?boolean} capture Check if the capture phase is supported.
 * @return {boolean} True if the event is supported.
 * @internal
 * @license Modernizr 3.0.0pre (Custom Build) | MIT
 */
function isEventSupported(eventNameSuffix, capture) {
  if (!ExecutionEnvironment.canUseDOM ||
      capture && !('addEventListener' in document)) {
    return false;
  }

  var eventName = 'on' + eventNameSuffix;
  var isSupported = eventName in document;

  if (!isSupported) {
    var element = document.createElement('div');
    element.setAttribute(eventName, 'return;');
    isSupported = typeof element[eventName] === 'function';
  }

  if (!isSupported && useHasFeature && eventNameSuffix === 'wheel') {
    // This is the only way to test support for the `wheel` event in IE9+.
    isSupported = document.implementation.hasFeature('Events.wheel', '3.0');
  }

  return isSupported;
}

module.exports = isEventSupported;