老师，请优化一下，谢谢

来源：3-25 编程练习

Moomin6

2019-05-27 14:19:23

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
<script>
    //补充代码
    function changeNum(str){
        for(var i = 0 ; i<7 ; i++){
            var num = str.charAt(i);
            str = str.replace(num,"*");
            }
        return str;
    }
    var num = prompt("请输入手机号码");
    document.write(changeNum(num));
</script>
</body>
</html>