js 验证码倒计时效果

function settime(obj) {
    if(second == 0){
        obj.removeAttribute("disabled");
        obj.value="获取验证码";
        second = 300;
        return;
    }else{
        obj.setAttribute("disabled", true);
        obj.value="重新发送(" + second + ")";
        second--;
    }
timeId = window.setTimeout(function(){settime(obj)},1000);
};

obj参数传入this即可。