js加减法

<html>
<head>
    <meta http-equiv="content-type" content='text/html;charset="utf-8"'>
    <script>
        function getRandom() {//孤风傲雪逗自己玩
            var rnd = Math.random();
            var number = Math.floor(rnd * 10);
            return number;
        }

        var a = getRandom();
        var b = getRandom();
        var aaa = a;
        var bbb = b;
        var aa = String(a);
        var bb = String(b);
        if (getRandom() % 2 == 0) {
            var c = a + b;
            var password = prompt(aa + "+" + bb + "=" + "?", "");
            if (password == c) {

                alert("正确");
            } else {
                alert("错误");
            }
        } else {
            var c = a - b;
            var password = prompt(aa + "-" + bb + "=" + "?", "");
            if (password == c) {

                alert("正确");
            } else {
                alert("错误");
            }


        }
    </script>
    
</head>
<body>
</body>
</html>