<script type="text/javascript">
var num=0;
function numCount(){
	document.getElementById('txt').value=num;
	num=num+1;
	setTimeout("numCount()",1000);
}
</script>

<pre class="html" name="code"><form>
	<input type="text" id="txt" />
	<input type="button" value="Start" onClick="numCount()" />
</form>
 

window.onload = function(){
    var num=0;
	var cishu = 0;//判斷函式執行次數
	document.getElementById('start').onclick = function(){
		++ cishu;
		if (cishu < 2) {
			startCount();
		}
	}
    function startCount() {
		document.getElementById('count').value = num;
		num=num+1;
		setTimeout(startCount, 1000);
	}
}
 

	window.onload = function(){
		var num=0;
		var cishu1 = 0;//判斷start點選函式執行次數
		var cishu2 = 1;//判斷stop點選函式執行次數
		var i;//用來傳遞setTimeout

		document.getElementById('start').onclick = function(){
			cishu2 = 0;
			if (cishu1 == cishu2) {
				startCount();
			}
			++ cishu1;
		}
		function startCount() {
			document.getElementById('count').value = num;
			num=num+1;
			i = setTimeout(startCount, 1000);
		}

		document.getElementById('stop').onclick = function(){
			cishu1 = 0;
			if (cishu1 == cishu2) {
				clearTimeout(i);
			}
			++ cishu2;
		}
	}