js判断浏览设备是 手机端，电脑端还是平板端

console.log(navigator.userAgent);

var os = function() {

    var ua = navigator.userAgent,

        isWindowsPhone = /(?:Windows Phone)/.test(ua),

        isSymbian = /(?:SymbianOS)/.test(ua) || isWindowsPhone,

        isAndroid = /(?:Android)/.test(ua),

        isFireFox = /(?:Firefox)/.test(ua),

        isChrome = /(?:Chrome|CriOS)/.test(ua),

        isTablet = /(?:iPad|PlayBook)/.test(ua) || (isAndroid && !/(?:Mobile)/.test(ua)) || (isFireFox && /(?:Tablet)/.test(ua)),

        isPhone = /(?:iPhone)/.test(ua) && !isTablet,

        isPc = !isPhone && !isAndroid && !isSymbian;

    return {

        isTablet: isTablet,

        isPhone: isPhone,

        isAndroid: isAndroid,

        isPc: isPc

    };

}();

if(os.isAndroid || os.isPhone) {

    alert("手机")

} else if(os.isTablet) {

    alert("平板")

} else if(os.isPc) {

    alert("电脑")

}