<script>
var obj;
var action;
function flash()
{
obj.style.background=obj.style.background=="#ffffff"?"#0000dd":"#ffffff"
}function begin(id)
{
obj=document.getElementById(id);
window.clearInterval(action);
action=window.setInterval("flash()",300);
}
function stop(x,y)
{
if(obj!=null)
obj.style.background="#ffffff"
window.clearInterval(action);
}
</script>
<table id=tb border=1 width=300 height=100>
<tr><td id = "flash1">1</td><td>2</td><td>3</td></tr>
<tr><td id = "flash4">4</td><td>5</td><td>6</td></tr>
<tr><td id = "flash7">7</td><td>8</td><td>9</td></tr>
</table>
<input type="button" value="开始" onclick="begin('flash4')">
<input type="button" value="停止" onclick="stop()">