怎么弄停止后繼續，繼續后還能停止
<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>計時器</title>
<script type="text/javascript">
function clock(){
var time = new Date();
document.getElementById("clock").value = time;
}
var i = setInterval(clock,100);
</script>
</head>
<body>
? <form>
? ? <input type="text" id="clock" size="50"? />
? ? <input type="button" value="Stop" onclick="clearInterval(i)"/>
? ? <input type="button" value="continue" onclick="setInterval(i)"">
? </form>
</body>
</html>
2019-09-24
<input type="button" value="continue" onclick="setInterval(clock,100);">
2019-10-09
<!DOCTYPE?HTML><html><head>? <meta?http-equiv="Content-Type"?content="text/html;?charset=utf-8">?? <title>計時器（暫停/開始）</title>?? <script?type="text/javascript">???? var?timer?=?null;???? ooop();???? function?ooop()?{?????? ????if?(!timer)?{ ????????timer?=?setInterval(?function?clock(){?????????? ????????????var?time?=?new?Date();?????????? ????????????document.getElementById("clock").value?=?time.getHours()+":"+time.getMinutes()+":"+time.getSeconds()?;;???????? ????????},?1000);?????? ?????}?else?{???????? ?????????clearInterval(timer)???????? ?????????timer?=?null;?????? ?????}???? ?}?? ?</script> ?</head> ?<body>?? ?<form>???? ?<input?type="text"?id="clock"?size="50"?/>???? ?<br?/>???? ?<input?type="button"?value="StopOrOpen"?onclick="ooop()"?/>?? ?</form> ?</body> ?</html>