js 发送短信验证码倒计时

html

<input type="button" id="btn" value="免费获取验证码" onclick="settime(this)" />

js

// 短信验证码倒计时
var countdown=60;
function settime(obj) {
    if (countdown == 0) {
        obj.removeAttribute("disabled");
        obj.value="免费获取验证码";
        countdown = 60;
        return;
    } else {
        obj.setAttribute("disabled", true);
        obj.value="重新发送(" + countdown + ")";
        countdown--;
    }
    setTimeout(function() {
            settime(obj) }
        ,1000)
}