方法1:

// 判断是访问的类型
function browserRedirect() {
    var sUserAgent = navigator.userAgent.toLowerCase();
    var bIsIpad = sUserAgent.match(/ipad/i) == "ipad";
    var bIsIphoneOs = sUserAgent.match(/iphone os/i) == "iphone os";
    var bIsMidp = sUserAgent.match(/midp/i) == "midp";
    var bIsUc7 = sUserAgent.match(/rv:1.2.3.4/i) == "rv:1.2.3.4";
    var bIsUc = sUserAgent.match(/ucweb/i) == "ucweb";
    var bIsAndroid = sUserAgent.match(/android/i) == "android";
    var bIsCE = sUserAgent.match(/windows ce/i) == "windows ce";
    var bIsWM = sUserAgent.match(/windows mobile/i) == "windows mobile";
    document.writeln("您的浏览设备为：");
    if (bIsIpad || bIsIphoneOs || bIsMidp || bIsUc7 || bIsUc || bIsAndroid || bIsCE || bIsWM) {
        location.href="https://www.baidu.com";
        // document.writeln("phone");
    }
    else {
        document.writeln("pc");
    }
}
browserRedirect();

方法2，使用正则来判断：

document.writeln("您的浏览设备为：");
 if(/Android|webOS|iPhone|iPod|BlackBerry/i.test(navigator.userAgent)) {
        document.writeln("phone");
    } else {
       document.writeln("pc");
    }

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