SimpleComet是一个轻量级的comet的封装类, 能智能的识别浏览器,应用不同的comet技术,在firefox浏览器上使用ajax，在IE、opera浏览器上使用htmlfile,iframe.

<script type="text/javascript"> // This function will be called every time the server pushes a new event. function push(event) { 	// For this example, we simply show the excuse on the page. 	document.getElementById('excuse').innerHTML = event; }   // This function will be called when/if the stream closes. function disconnected() { 	// For this example we'll just show a nice message. 	document.getElementById('excuse').innerHTML = '<img src="img/arrow.png" alt="" title="" />'+ 		' Click to see MORE reasons why this souldn\'t work!'; 	document.getElementById('control').value = 'start'; }   // This function is executed when the button is clicked. function toggle() { 	// First we check if the stream is open. 	if (!comet.active) { 		// Lets start streaming! 		comet.open('excuses.php', push, disconnected); 		document.getElementById('control').value = 'stop'; 	} else { 		// Streaming is active, means the user wants to stop it. 		comet.close(); 	} } </script>

<!--?php   // First we load the SimpleComet PHP class and the list of excuses. require('inc/simplecomet.class.php'); $comet = new SimpleComet(); $excuses = file('inc/excuses.txt');   // This is an infinite loop, which makes the stream endless. while (true) { 	// We fetch an excuse at random. 	$excuse = trim($excuses[rand(0, count($excuses))]); 	// If the excuse is too long, we get another one. 	if (strlen($excuse) --> 60) { continue; } 	// Finally, we push our excuse to the client. 	$comet->push($excuse); 	// 5 seconds delay before the next excuse. 	sleep(5); }   ?>

simplecomet能监听出链接是否已经断了,是不是很智能，只要负责服务端的输出就行. 
下载: http://www.mandor.net/files/simplecomet-1.0.zip