Eli Grey

XDomainRequest is no longer IE-only

XDomainRequest is Internet Explorer 8’s cross-domain request function. It would be easy to add support for it in Firefox 3.5 using native cross-domain XMLHttpRequests, but that wouldn’t work in Firefox 3, Opera 9.6-10, and Safari 4. I have created a library named XXDomainRequest (means “Cross-browser XDomainRequest”) that builds on the pmxdr client library to create a fully API compatible version of XDomainRequest. Go to the XXDomainRequest project page to see (and run) the examples that request resources on code.eligrey.com.

Reusable pmxdr instances

I just released version 0.0.4 of the pmxdr client code to support reusable instances where the same iframe can be used for mutiple pmxdr requests to a domain. It’s still the same interface, but you need to call pmxdr.request() instead of pmxdr() to do a normal request. Instances are created with new pmxdr(host) where host is any URI from the website you want to request (pmxdr figures out where the API is located automatically). Then just call the request method on the instance once the interface iframe has loaded, which you can find out when instance calls it’s onload method once it’s loaded if you set it. The request method now also accepts an array of requests. To start loading the instance, you call it’s init method. To remove the interface frame, you call it’s unload method. Another thing added is the ability to completely remove pmxdr using its destruct method, which removes all event listeners and deletes the pmxdr variable. This does not delete any still-existing interface frames so don’t forget to unload them when you are done to avoid memory leaks.

Using reusable instances saves much more overhead than repeatedly re-requesting a website’s pmxdr host api. When I updated the demo to use a single instance for requesting eligrey.com, it started finishing a multitude of times faster. This is an example of using a reusable instance that uses one interface to make three requests:

var exampleDotCom = new pmxdr("http://example.com");
exampleDotCom.onload = function() {
      uri     : "/foo.html",
      callback: responseHandlers.foo
      uri     : "/bar.html",
      callback: responseHandlers.bar
      uri     : "/baz.html",
      callback: responseHandlers.baz
// after all responseHandlers[x] are called, call exampleDotCom.unload()

pmxdr standard documented

I decided to make some detailed documentation on the pmxdr standard used for pmxdr client and host interaction. You may use the standard to implement your own pmxdr client and host libraries. This is particularly useful for websites that don’t want to follow any HTTP access control headers and want to make their own host library implementation use different methods of verification than the reference implementations. The standard is dedicated to the public domain just like every standard I have released so far.

I also modified the demo to automatically do every test so you don’t have to click any buttons to initiate tests.

pmxdr: postMessage cross-domain request library

pmxdr is a cross-domain HTTP request JavaScript library. pmxdr stands for postMessage cross-domain requester. As the name implies, it makes use of the HTML5 postMessage API to make HTTP requests. It requires that a pmxdr host be on the target domain and it respects all HTTP access control headers, even on browsers that don’t support them but do support postMessage, like Firefox 3.

You can download the pmxdr client library and the pmxdr host library (includes an example .htaccess file to help Apache users with PHP set it up) under the latest GNU GPL license and an MIT-style license. The host library must be able to be accessed from /pmxdr/api to be able to interact with the client library.

Read more at the pmxdr project page and try out the demo of it in action.

The following is a very simple example of how to use pmxdr to do a cross-domain POST request (impossible with the normal method of inserting a script tag):

// The requesting domain is example.net
// example.net doesn't want to give any control to example.com
  method   : "post",
  uri      : "http://example.com/search.json",
  data     : "q=foo",
  callback : loadSearchJSON

Usually, in this hypothetical example, example.net would have to put a script tag with an src of http://example.com/search.json?q=foo&callback=loadSearchJSON and give example.com full control of example.net. This provides a secure cross-domain way to use APIs like this.