js判断是哪个浏览器
var inBrowser = typeof window !== 'undefined';
var inWeex = typeof WXEnvironment !== 'undefined' && !!WXEnvironment.platform;
var weexPlatform = inWeex && WXEnvironment.platform.toLowerCase();
var UA = inBrowser && window.navigator.userAgent.toLowerCase();
var isIE = UA && /msie|trident/.test(UA);
var isIE9 = UA && UA.indexOf('msie 9.0') > 0;
var isEdge = UA && UA.indexOf('edge/') > 0;
var isAndroid = (UA && UA.indexOf('android') > 0) || (weexPlatform === 'android');
var isIOS = (UA && /iphone|ipad|ipod|ios/.test(UA)) || (weexPlatform === 'ios');
var isChrome = UA && /chrome\/\d+/.test(UA) && !isEdge;