源代码：
html文件
<html>
<head>
<title>表单验证码</title>
<script type = "text/javascript" src = "js/checkCode.js"></script>
</head>
<body>
<div>
<input type = "text" id = "input"/> <br />
<input type = "button" id="code" onclick="createCode()"/>
<input type = "button" value = "验证" onclick = "validate()"/>
</div>
</body>
</html>
css文件
#code {
font-family:Arial;
font-style:italic;
font-weight:bold;
border:0;
letter-spacing:2px;
color:blue;
}
js文件
var code ; //在全局定义验证码
//产生验证码
window.onload = createCode;
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');//随机数
for(var i = 0; i < codeLength; i++) {//循环操作
var index = Math.floor(Math.random()*36);//取得随机数的索引（0~35）
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
function validate(){
var inputCode = document.getElementById("input").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
}
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
document.getElementById("input").value = "";//清空文本框
}
else { //输入正确时
alert("验证码输入正确");
}
}
验证码预览图.png
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