发送验证码后倒计时功能实现

function settime(obj) {
    if (countdown == 0) {
        obj.removeAttribute("disabled");
        var txt = "获取验证码";
        $(obj).text(txt);
        countdown = 60;
        return;
    } else {
        obj.setAttribute("disabled", true);
        var txt = "重新发送(" + countdown + ")";
        $(obj).text(txt);
        countdown--;
    }

    setTimeout(function() {
            settime(obj)
    }, 1000);
}

<button class="btn_yan" onclick="settime(this); return false;">获取验证码</button>

<script>

var countdown = 60;

</script>