performanceNow.js

/**
 * Copyright 2013 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule performanceNow
 * @typechecks static-only
 */

"use strict";

var ExecutionEnvironment = require('ExecutionEnvironment');

/**
 * Detect if we can use window.performance.now() and gracefully
 * fallback to Date.now() if it doesn't exist.
 * We need to support Firefox < 15 for now due to Facebook's webdriver
 * infrastructure.
 */
var performance = null;

if (ExecutionEnvironment.canUseDOM) {
  performance = window.performance || window.webkitPerformance;
}

if (!performance || !performance.now) {
  performance = Date;
}

var performanceNow = performance.now.bind(performance);

module.exports = performanceNow;