判断访问设备类型（android、ios、微信、pc）

var u = navigator.userAgent, app = navigator.appVersion;
var isAndroid = u.indexOf('Android') > -1 || u.indexOf('Linux') > -1;
var isIOS = !!u.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/);
var isWechat = u.match(/MicroMessenger/i) == 'micromessenger';