JavaScript 简单定时器原理

  <input type="button" value="开始计时！" onclick="timedCount()">
    <input type="text" id="txt">
    <input type="button" value="停止计时！" onclick="stopCount()">
    <script type="text/javascript">
        var c = 0;
        var t;
        timedCount();
        function timedCount() {
            document.getElementById('txt').value = c;
            c = c + 1;
            t = setTimeout("timedCount()", 1000);
        }

        function stopCount() {
            clearTimeout(t);
        }

    </script>