javascript实现登录验证码

<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Document</title>
</head>
 <body onload="createCode();">
    <input type="text" value="" id="checkNum" />
    <a id="checkCode" onclick="createCode()"></a>
    <input type="button" class="btnCheck" id="gotoCheck"  value="验证"  onclick="validate();" />
    <script>
    var code="" ; //在全局 定义验证码
    function createCode(){
    code = "";
    var codeLength = 6;//验证码的长度
    var checkCode = document.getElementById("checkCode");
    checkCode.value = "";
    var selectChar = new Array(0,1,2,3,4,5,6,7,8,9,'A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z');


    for(var i=0;i<codeLength;i++) {
       var charIndex = Math.floor(Math.random()*35);
       code +=selectChar[charIndex];
    }
    if(code.length != codeLength){
       createCode();
    }
    document.getElementById("checkCode").innerHTML = code;
    }

    function validate () {
    var inputCode = document.getElementById("checkNum").value.toUpperCase();


    if(inputCode.length <=0) {
       alert("请输入验证码!");
       return false;
    }
    else if(inputCode != code ){
       alert("验证码输入错误!");
       createCode();
       return false;
    }
    else {
       alert("验证码通过!");
       return true;
    }
    }
    </script>
</body>
</html>

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转载自blog.csdn.net/daimomo000/article/details/79353480
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