Javascript实现计时和停止计时

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
        <title>计时器</title>
        
        <script type="text/javascript">
        var sec = 0;
        //设置计时器
        var timeId = setInterval("count();",1000);