Cross-Browser XMLHttpRequest

Opera 7.60(beta) supports `XMLHttpRequest`!

Support for XMLHttpRequest has been added to Opera 7.60. My code is still useful for older versions of Opera (and maybe for other browsers too), so I'm going to leave this page here.

Introduction

Opera's Lack of `XMLHttpRequest` Support

This started off when Google announced their Gmail product. The two most used browsers, IE and Mozilla/Firefox, were supported, but not the third most used browser, Opera. The main reason seemed to be Opera's lack of support for the Mozilla/Gecko XMLHttpRequest object, itself modelled on Microsoft's XMLHTTP ActiveX object.

Naturally, there were immediate calls for Opera Software to implement XMLHttpRequest. As with all software development, this takes time to implement and test, so Opera is not expected to support it immediately.

With some help, this module has allowed Opera to work with Gmail. See my Opera Gmail page.

Equivalent Functionality

All this started when Mendrik posted (Opera newsserver or Google Groups Beta) some Javascript that emulated the functionality of the XMLHttpRequest GET request. The code was compatible with IE, Mozilla/Firefox and Opera.

Faking It

That code worked, but it wasn't call or usage compatible with existing code that used XMLHttpRequest. It occurred to me that it might be possible to develop some Javascript that would provide an emulation of a real XMLHttpRequest object. The code I developed provides a workable, but not perfect, emulation.

I expect Opera Software to soon develop native support for XMLHttpRequest, so my code is simply a stop gap measure for now.

While I originally intended to give only Opera support for XMLHttpRequest, I noticed that it was trivial to add support for Internet Explorer too. Having added that, I noticed it was just as trivial to add basic ActiveXObject emulation for "XMLHTTP" too. So now your web pages can use either the Microsoft or the Gecko-style API and with care they'll work without modification for Internet Explorer, Mozilla/Gecko, and Opera.

When/if Internet Explorer and/or Opera eventually natively support XMLHttpRequest my code will automatically use that instead, but you might want to keep my code around for a bit to support people who haven't updated.

Download

This work is licensed under a Creative Commons License.

Attribution under the above license: Leave my name and web address in the script intact.

xmlhttprequest.js - Cross-browser XMLHttpRequest Javascript module v1.2 2005-06-14 (8393)

Demonstration

Load this demonstration's Javascript source code into the space below.

Description

Requirements

The Opera browser support requires a Java Runtime Environment. Although the code developed by Mendrik shows that it's possible to emulate GET requests without Java, POST requests have proved to be impossible to support without Java. As POST support is half the functionality, I decided to use Java code for both GET and POST.

Usage

Add the script to the <HEAD> section of your web page:

<script type="text/javascript" src="xmlhttprequest.js"></script>

Then write your code following the Gecko XMLHttpRequest API.

GET Requests

Example:

var req = new XMLHttpRequest(); if (req) { req.onreadystatechange = function() { if (req.readyState == 4 && (req.status == 200 || req.status == 304)) { alert(req.responseText); } }; req.open('GET', 'pageurl.html'); req.send(null); }

POST Requests

Example:

var req = new XMLHttpRequest(); if (req) { req.onreadystatechange = function() { if (req.readyState == 4 && (req.status == 200 || req.status == 304)) { alert(req.responseText); } }; req.open('POST', 'scripturl.cgi'); // many server-side scripts require the Content-Type to be set: req.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8'); req.send('var1=data1&var2=data2'); }

"Connection failed" security exceptions

These have puzzled me for a while. They have now been explained to me by "Rolf PK" who has determined that default Opera security policy settings may be preventing the connection. These need to be overridden in the opera.policy file. In the "grant" section, you need to add:

// for access to regular web servers (port 80) permission java.net.SocketPermission "*:80", "connect,resolve"; // for access to secure servers (port 443) permission java.net.SocketPermission "*:443", "connect,resolve";

Thanks Rolf!

Unsupported Functionality

The Opera code does not support:

User/password authentication.
The responseXML data member.
Asynchronous requests are not properly supported. This appears to be because the Opera Javascript interpreter is single-threaded. The send() method will return immediately, but the actual async request will not occur until the current execution context ends. For example, if you follow send() with a long sequence of processing, the request will still not have been sent by the time it finishes.
abort() is not fully supported either. A consequence of the single-threaded nature of Opera's Javascript interpreter is that once the request starts it cannot be stopped until it completes.
The getAllResponseHeaders and getAllResponseHeader methods are not fully supported. For me, at least, no response header information was available via the expected Java methods, so I've had to write some fallback code to get some limited header information from alternative methods.

Version History

XMLHttpRequest Javascript Version History
Version	Date	Description
n/a	2005-09-28	Added notes in relation to the "Connection failed" security exceptions.
1.2	2005-03-30	Added `getResponseHeader`.
n/a	2004-08-24	Opera 7.60 has added support for `XMLHttpRequest`.
1.1	2004-06-26	Added ActiveXObject emulation.
1.0	2004-06-24	Initial release.

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