JQ 验证码倒计时

// 验证码 限制4位数
<div class="yam">
                    <input value="" oninput="if(value.length>4)value=value.slice(0,4);if(value<0)value=0" type="number" placeholder="验证码" />
                    <input style="background: #FFFFFF;color: #f2921b;" type="button" id="btn" value="获取验证码" onclick="Verification()" /> 
                </div>

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 + ")");
        obj.css({
            color:'#bababa'
        })
        countdown--;
    }
    setTimeout(function() {
        settime(obj)
    }, 1000)
}

// 点击获取验证码
function Verification() {
    let html = $('#mobile').val()
    var obj = $("#btn");
    settime(obj);
    console.log(html)
}