验证码倒计时

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<script src="http://libs.baidu.com/jquery/1.10.2/jquery.min.js"></script>
<script type="text/javascript"> 
var countdown=60; 
function sendemail(){
    var obj = $("#btn");
    settime(obj);
    }
function settime(obj) { //发送验证码倒计时
    if (countdown == 0) { 
        obj.attr('disabled',false); 
        //obj.removeattr("disabled"); 
        obj.val("免费获取验证码");
        countdown = 60; 
        return;
    } else { 
        obj.attr('disabled',true);
        obj.val("重新发送(" + countdown + ")");
        countdown--; 
    } 
setTimeout(function() { 
    settime(obj) }
    ,1000) 
}
</script>
<body> 
<input type="button" id="btn" value="免费获取验证码" onclick="sendemail()" /> 
</body>
</html>
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