JavaScript生成简单数字验证码

<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport"
          content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Title</title>
</head>
<body>
<p class="code"></p>
<button>生成验证码</button>

<script>
    //验证码函数
    function createCode(length) {//验证码长度
        var code = "";
        for (var i = 1; i <= length; i++) {
            code += (parseInt(Math.random() * 10));
        }

        return code;
    }

    //输出函数
    function deal() {
        document.getElementsByClassName("code")[0].innerText = "生成的验证码:" + createCode(4);
    }

    //事件处理
    document.getElementsByTagName("button")[0].onclick = deal;
</script>
</body>
</html>