The keystone of AJAX is the XMLHttpRequest object.
All modern browsers support the XMLHttpRequest object.
The XMLHttpRequest object is used to exchange data with a server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
All modern browsers (Chrome, IE7+, Firefox, Safari, and Opera) have a built-in XMLHttpRequest object.
Syntax for creating an XMLHttpRequest object:
variable = new XMLHttpRequest();
Old versions of Internet Explorer (IE5 and IE6) use an ActiveX Object:
variable = new ActiveXObject("Microsoft.XMLHTTP");
To handle all browsers, including IE5 and IE6, check if the browser supports the XMLHttpRequest object. If it does, create an XMLHttpRequest object, if not, create an ActiveXObject:
var xhttp;
if (window.XMLHttpRequest) {
xhttp = new XMLHttpRequest();
}
else {
// code for IE6, IE5
xhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
Try it Yourself »
For security reasons, modern browsers do not allow access across domains.
This means that both the web page and the XML file it tries to load, must be located on the same server.
The examples on W3Schools all open XML files located on the W3Schools domain.
If you want to use the example above on one of your own web pages, the XML files you load must be located on your own server.
Old versions of Internet Explorer (IE5 and IE6) do not support the XMLHttpRequest object.
To handle IE5 and IE6, check if the browser supports the XMLHttpRequest object, or else create an ActiveXObject:
if (window.XMLHttpRequest) {
// code for modern browsers
xmlhttp = new XMLHttpRequest();
}
else {
// code for old IE browsers
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
Try it Yourself »
| Method | 説明 |
|---|---|
| new XMLHttpRequest() | Creates a new XMLHttpRequest object |
| abort() | Cancels the current request |
| getAllResponseHeaders() | Returns header information |
| getResponseHeader() | Returns specific header information |
| open(method,url,async,user,psw) | Specifies the request method: the request type GET or POST url: the file location async: true (asynchronous) or false (synchronous) user: optional user name psw: optional password |
| send() | Sends the request to the server Used for GET requests |
| send(string) | Sends the request to the server. Used for POST requests |
| setRequestHeader() | Adds a label/value pair to the header to be sent |
| Property | 説明 |
|---|---|
| onreadystatechange | Defines a function to be called when the readyState property changes |
| readyState | Holds the status of the XMLHttpRequest. 0: request not initialized 1: server connection established 2: request received 3: processing request 4: request finished and response is ready |
| responseText | Returns the response data as a string |
| responseXML | Returns the response data as XML data |
| status | Returns the status-number of a request 200: "OK" 403: "Forbidden" 404: "Not Found" For a complete list go to the Http Messages Reference |
| statusText | Returns the status-text (e.g. "OK" or "Not Found") |