Javascript 擷取驗證碼60秒倒計時

<button id="time">擷取驗證碼</button>var countdown = 60;var but = document.getElementById('time');but.addEventListener('click', function (e) {    setTime(this);})function setTime (elem) {    if (countdown === 0) {        elem.innerHTML = "擷取驗證碼";        countdown = 5;        elem.disabled = false;        clearTimeout(anima);    } else {        countdown--;        elem.innerHTML = "重新擷取(" + countdown + ")";                elem.disabled = true;        var anima = setTimeout(function () {            setTime(elem);        }, 1000);    }}