javascript实现动态验证码功能


<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"/>
</head>
<body>
<dl class="admin_login">
    <form action="#" method="post">
        <input type='hidden' name='codes' id='codes'>
        <dd class="user_icon">
            <input type="text" placeholder="账号" name="name" class="login_txtbx"/>
        </dd>
     <dd class="pwd_icon">
            <input type="password" placeholder="密码" name="paws" class="login_txtbx"/>
        </dd>
        <dd class="val_icon">
            <div class="checkcode">
                <input type="text" id="J_codetext" name='code' placeholder="验证码" maxlength="4" class="login_txtbx">
                <canvas class="J_codeimg" id="myCanvas" onclick="createCode()">对不起，您的浏览器不支持canvas，请下载最新版浏览器!</canvas>
            </div>
            <input type="button" value="更换验证码" class="ver_btn" onClick="validate();">
        </dd>
        <dd>
            <input type="submit" value="立即登陆" class="submit_btn"/>
        </dd>
</form>
</dl>
</body>
<script type=text/javascript>
$(document).ready(function() {
      //验证码
      createCode();
});
//生成画布
function showCheck(a){
    var c = document.getElementById("myCanvas");
        var ctx = c.getContext("2d");
    ctx.clearRect(0,0,1000,1000);
    ctx.font = "80px 'Microsoft Yahei'";
    ctx.fillText(a,0,100);
    ctx.fillStyle = "white";
}
//生成验证码的文字
var code ;    
function createCode(){       
    code = "";      
    var codeLength = 4;
    var selectChar = new Array(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','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()*60);      
      code +=selectChar[charIndex];
    }      
    if(code.length != codeLength){      
      createCode();      
    }
    showCheck(code);
    document.getElementById("codes").value=code;
}
//验证码较验
function validate () {
    var inputCode = document.getElementById("J_codetext").value.toUpperCase();
    var codeToUp=code.toUpperCase();
    if(inputCode.length <=0) {
      document.getElementById("J_codetext").setAttribute("placeholder","请输入验证码  ");
      createCode();
      return false;
    }
    else if(inputCode != codeToUp ){
      document.getElementById("J_codetext").value="";
      document.getElementById("J_codetext").setAttribute("placeholder","请输入正确的验证码");
      createCode();
      return false;
    }
    else {
      window.open(document.getElementById("J_down").getAttribute("data-link"));
      document.getElementById("J_codetext").value="";
      createCode();
      return true;
    }

}
</script>
</html>
javascript实现动态验证码功能

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