获取XMLHttpRequest的步骤

添加评论 11 views 2009年6月22日

step 1: trigger an event to call a javascript function
step 2. create XMLHttpRequest Object
step 3. open a web resource
step 4. register a callback on xhr
step 5. send request

举例:

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< !DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>First Ajax Program Using XHR</title>
<script type="text/javascript">
	var xhr = null;
	function getData(){
		//step 2. create XMLHttpRequest Object
		xhr = createXhr();
		//step 3. open a web resource
		xhr.open("GET","data.txt");
		//step 4. register a callback on xhr
		xhr.onreadystatechange = display;
		//step 5. send request
		xhr.send(null);
	}
 
	//handle response
	function display(){
		if(xhr.readyState == 4){
			if(xhr.status == 200){ //end in success
				document.getElementById("data").innerHTML 
				   = xhr.responseText;
			}else{
				alert("Error: " + xhr.status + " " + xhr.statusText);
			}
		}else{
			document.getElementById("data").innerHTML 
				   = "loading...";
		}
	}
 
	function createXhr(){
		if(window.ActiveXObject){           //IE browser
			return new ActiveXObject("Microsoft.XMLHTTP");
		}else if(window.XMLHttpRequest){         //other browsers support ajax
			return new XMLHttpRequest();
		}else{                            //browsers don't support ajax
			throw new Error("Does not support ajax program");
		}
	}
</script>
</meta></head>
<!--step 1: trigger an event to call a javascript function -->
<body onload="getData()">
	<div id="data"></div>
</body>
</html>
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