基础

重复调用的定时器

var timer = null;

if (timer) clearInterval(timer);
fun();
timer = setInterval(fun,1000);
function fun(){
        
}
if (timer) clearInterval(timer);

只调用一次的定时器

setTimeout(function () {

},5000);

倒计时

window.onload = function () {

    var oOldDate = new Date("2016/8/8 23:30:30");
    var oNewDate = new Date("2016/8/9 00:00:00");
    var nChaZhi = oNewDate.getTime()-oOldDate.getTime();
    var chaMiao = 1000;
    var chaFen = chaMiao*60;
    var chaShi = chaFen*60;

    var timer = null;
    if (timer) clearInterval(timer);
    funShowTime();
    timer = setInterval(funShowTime,1000);
    function funShowTime(){
        nChaZhi-=1000;
        var miao = parseInt(nChaZhi%chaFen/chaMiao);
        var fen = parseInt(nChaZhi%chaShi/chaFen);
        var shi = parseInt(nChaZhi/chaShi);
        console.log(shi+"时"+fen+"分"+miao+"秒");
        if (nChaZhi==0){
            if (timer) clearInterval(timer);
        }
    }

}

短信倒计时

<div id="box" class="box">
    <input type="text" />
    <button>点击发送短信</button>
</div>

* {
    margin: 0;
    padding: 0;
}
.box {
    margin: 100px 100px;
}

window.onload = function () {

    var oBox = document.getElementById("box");
    var oInput = oBox.getElementsByTagName("input")[0];
    var oButton = oBox.getElementsByTagName("button")[0];

    var timer = null;
    oButton.onclick = function() {
        var nChaZhi = 10;

        var that = this;
        if (timer) clearInterval(timer);
        funSendMessage();
        timer = setInterval(funSendMessage,1000);
        function funSendMessage(){
            if (nChaZhi>=0) {
                that.disabled = nChaZhi;
                that.innerHTML = "剩余"+nChaZhi+"秒";
                if (nChaZhi==0){
                    that.innerHTML = "重新发送短信";
                    if (timer) clearInterval(timer);
                }
            }
            nChaZhi--;
        }
    }

}