随机验证码

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #box{
            width: 100px;
            height: 40px;
            background: #b0b0b0;
            font-size: 30px;
            font-weight: bold;
            line-height: 40px;
            text-align: center;
            margin: 50px auto;
        }
    </style>
</head>
<body>
    <div id="box">8pxY</div>
    <script>
        var str = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';//0-61
//        获取四位随机字符
        function change() {
            var str1 = '';
            for (var i = 0; i < 4; i++){
                str1 += str[getRandom(0,61)];
            }
            document.getElementById('box').innerHTML = str1;
        }
        change();
        document.getElementById('box').onclick = change;
//        获取随机数方法
        function getRandom(n,m) {
            if(n > m){
                var temp = n;
                n = m;
                m = temp;
            }
            n = Math.ceil(n);
            m = Math.floor(m);
            return Math.round(Math.random()*(m-n)+n);
        }
    </script>
</body>
</html>