XMLHttpRequest object
The XMLHttpRequest object is the core of Ajax technology.
All modern browsers support the XMLHttpRequest object (IE5 and IE6 use ActiveXObject).
Interacting with the server without refreshing the page is the biggest feature of Ajax. This important feature is mainly due to the XMLHttpRequest object. Using the XMLHttpRequest object enables web applications, like windows applications, to respond promptly to interactions between users and servers without having to refresh or jump the page, and to perform a series of data processing. These functions can shorten the user's waiting time. , and also reduces the load on the server side.
Create XMLHttpRequest object
Modern browsers (IE7+, Firefox, Chrome, Safari and Opera) all have built-in XMLHttpRequest objects.
Syntax for creating XMLHttpRequest objects:
variable=new XMLHttpRequest();
Older versions of Internet Explorer (IE5 and IE6) use ActiveX objects ：
variable=new ActiveXObject("Microsoft.XMLHTTP");
To cope with all modern browsers, including IE5 and IE6, please check whether the browser supports XMLHttpRequest object. If supported, creates an XMLHttpRequest object. If not supported, create an ActiveXObject: :
<!DOCTYPE html>
<html>
<head>
<script>
function loadXMLDoc()
{
var xmlhttp;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
document.getElementById("myDiv").innerHTML=xmlhttp.responseText;
}
}
xmlhttp.open("GET","/try/ajax/ajax_info.txt",true);
xmlhttp.send();
}
</script>
</head>
<body>
<div id="myDiv"><h2>使用AJAX</h2></div>
<button type="button" onclick="loadXMLDoc()">点击修改</button>
</body>
</html>