<!DOCTYPE html>
<html>
<head>
<title>纯js验证码</title>
</head>
<style>
#code{font-family:Arial; font-style:italic; font-weight:bold; border:0; letter-spacing:2px; color:blue; }
</style>
<script src="https://lib.baomitu.com/jquery/3.4.1/jquery.js"></script>
<body>
<div style="300px;">
<span class="web-form-span " >验证码：</span>
<input type="text" class=" web-form-input " required="required" id="Yzm" style=" 30%;float: initial;" >
<input type = "button" id="code" value="点我验证" class="btn-list-btn" onclick="createCode()"/>
</div>
</body>
<script>
//在全局定义验证码
var code;
//产生验证码
function createCode(){
code = "";
var codeLength = 4;//验证码的长度
var checkCode = document.getElementById("code");
var random = new Array(0,1,2,3,4,5,6,7,8,9,
'A','B','C','D','E','F','G','H','I','J','K','L','M',
'N','O','P','Q','R', 'S','T','U','V','W','X','Y','Z',
'a','b','c','d','e','f','g','h','i','j','k','l','m',
'n','o','p','q','r','s','t','u','v','w','x','y','z');//随机数
for(var i = 0; i < codeLength; i++) {//循环操作
var index = Math.floor(Math.random()*62);//取得随机数的索引（0~61）
code += random[index];//根据索引取得随机数加到code上
}
checkCode.value = code;//把code值赋给验证码
}
//校验验证码
document.getElementById("Yzm").addEventListener("change",validate);
//验证事件
function validate(){
var inputCode = document.getElementById("Yzm").value.toUpperCase(); //取得输入的验证码并转化为大写
if(inputCode.length <= 0) { //若输入的验证码长度为0
alert("请输入验证码！"); //则弹出请输入验证码
$("#Yzm").focus();
YZM = false;
} else if(inputCode != code ) { //若输入的验证码与产生的验证码不一致时
alert("验证码输入错误！@_@"); //则弹出验证码输入错误
createCode();//刷新验证码
$("#Yzm").val("");//清空文本框
$("#Yzm").focus();//重新聚焦验证码框
YZM = false;
} else { //输入正确时
$("#Yzm").blur();//绑定验证码输入正确时要做的事
YZM = true;
alert("验证码正确！");
}
};
</script>
</html>