点击按钮实现倒计时

<input type="button" class="pro-button" id="btn"
                       style="color: red; background-color: #FFFAFA;margin-top: 0;"
                       onclick="setTime(this)" value="获取验证码">

var countDown=60;
function setTime(val) {
    if (countDown == 0) {
        val.removeAttribute("disabled");
        val.value = "获取验证码";
        countDown = 60;
        return;
    } else {
        val.setAttribute("disabled", true);
        val.value = "重新发送(" + countDown + ")";
        countDown--;
    }
    setTimeout(function () {
        setTime(val)
    }, 1000)
}