Javascript 獲取驗證碼60秒倒計

<button id="time">獲取驗證碼</button>

var countdown = 60;
var but = document.getElementById('time');
but.addEventListener('click', function (e) {
    setTime(this);
})

function setTime (elem) {
    if (countdown === 0) {
        elem.innerHTML = "獲取驗證碼";
        countdown = 60;
        elem.disabled = false;
        clearTimeout(anima);
    } else {
        countdown--;
        elem.innerHTML = "重新獲取(" + countdown + ")";        
        elem.disabled = true;
        var anima = setTimeout(function () {
            setTime(elem);
        }, 1000);
    }
}