setTimeout("函数","未来指定毫秒后调用函数");
clearTimeout(setTimeout("函数","未来指定毫秒后调用函数"));
<!DOCTYPE html>
<html><head><meta charset="utf-8"><title></title></head><body><button onclick="starTime()">开始</button><button onclick="stopTime()">停止</button><script>var t;function fun() {alert("Hello World");}function starTime() {t=setTimeout("fun()",300);}function stopTime(){clearTimeout(t);alert(t);}</script></body>
</html>setInterval("fun()",3000);每隔指定时间调用
clearInterval(t);取消setIntval()
<!DOCTYPE html>
<html><head><meta charset="utf-8"><title></title></head><body><button onclick="starTime()">开始</button><button onclick="stopTime()">停止</button><script>var t;function fun() {alert("Hello World");}function starTime() {t=setInterval("fun()",3000);}function stopTime(){clearInterval(t);alert(t);}</script></body>
</html>计时器：
三个功能 开始 复位 停止
<!DOCTYPE html>
<html><head><meta charset="utf-8"><title></title><style>div {height: 50px;width: 100px;background-color: skyblue;padding: auto;text-align: center;line-height: 50px;border: 2px solid black;position: relative;cursor: pointer;border-radius: 5px;font-weight: 200px;font-size: 20px;}.start {top: 100px;right: -500px;}.stop {top: 45px;right: -700px;}.zero {top: -100px;right: -600px;}.time {height: 100px;width: 300px;top: 50px;right: -500px;font-size: 80px;text-align: center;line-height: 100px;font-family: "宋体";font-weight: 1000;}div:hover {background-color: darkgray;}</style></head><body><div class="start" onclick="start()">开始</div><div class="stop" onclick="stop()">停止</div><div class="zero" onclick="reset()">复位</div><div class="time" id="time">0</div><script>var s = 0;var t;function start() //开始计时{if (!t)t = setInterval("change()", 1000);}function reset() //复位{clearInterval(t);s = -1;change();t = null;}function stop() // 停止计时{clearInterval(t);t = null;}function change() {s++;var x = document.getElementById("time");x.innerHTML = s;}</script></body>
</html>电子钟：每秒更新一次页面
<!DOCTYPE html>
<html><head><meta charset="utf-8"><title>电子表</title><style>.table {height: 100px;width: 500px;background-color: grey;text-align: center;margin: auto;border-radius: 5px;border: 4px solid black;font-size: 20px;}</style><script>function updateTime() {var date = new Date();document.getElementById("year").innerText = date.getFullYear();document.getElementById("month").innerText = date.getMonth() + 1;document.getElementById("day").innerText = date.getDate();document.getElementById("hour").innerText = date.getHours();document.getElementById("minutes").innerText = date.getMinutes();document.getElementById("second").innerText = date.getSeconds();}setInterval(updateTime, 1000);</script></head><body onload="updateTime()"><table class="table"><th id="year"></th><th>年</th><th id="month"></th><th>月</th><th id="day"></th><th>日</th><th id="hour"></th><th>:</th><th id="minutes"></th><th>:</th><th id="second"></th></table></body>
</html>
