使用javascript定时器定时调用一个function，不能用SetTimer，要使用setInterval

    <html>
    <head>
    <script language="javascript">
    var timerHandle;
    // invoke alertalertalert every 1 seconds
    timerHandle = setInterval("alertalertalert()", 1000);

    function alertalertalert() {
        document.getElementById("tthandle").value = document.getElementById("tthandle").value + "Hello here." + "\n";
    }

    function releaseTimer() {
        clearInterval(timerHandle);
    }
    </script>
    <body onunload="releaseTimer()">
    <textarea cols="100" rows="10" readonly id="tthandle"></textarea>
    </body>
    </html>