判断运行环境
const inBrowser = typeof window !== 'undefined' const inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform const weexPlatform = inWeex && WXEnvironment.platform.toLowerCase() const UA = inBrowser && window.navigator.userAgent.toLowerCase() const isIE = UA && /msie|trident/.test(UA) const isIE9 = UA && UA.indexOf('msie 9.0') > 0 const isEdge = UA && UA.indexOf('edge/') > 0 const isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android') const isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios') const isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge const isPhantomJS = UA && /phantomjs/.test(UA) const isFF = UA && UA.match(/firefox\/(\d+)/)