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")
}