CORS.js

A small (1.85KB minified and gzipped) cross-browser library to support Cross Origin Resource Sharing requests. The script exposes two global constructors; window.CORS and window.JSONPHttpRequest.

window.CORS

Acts as a wrapper around the transport used to communicate across origins. The transport is automatically chosen from what the browser supports, either XMLHttpRequest v2 (newer browsers) or XDomainRequest (IE 8 - 9) or JSONPHttpRequest (all others).

Parameters

• forceJSONP (boolean, optional, default false) Forces the use of the JSONPHttpRequest object as the transport even if the browser can use XMLHttpRequest v2 or XDomainRequest (useful for script loading).

var cors = new CORS(true);

window.JSONPHttpRequest

This is used as a fallback for browsers that support neither XMLHttpRequest v2 or XDomainRequest and supports the same methods.

Usage

Invoke as if using XMLHttpRequest. That's it.

The same methods and properties as XMLHttpRequest are available and use the same parameters. readyState and status are updated as necessary on the object and onreadystatechange is settable and is invoked appropriately.

Example

var request = new CORS();

request.onreadystatechange = function () { // 'this' is the CORS object
    var text;

    if (this.readyState === 4) {
        text = this.responseText;
        // do something with the response
    }
};
request.open('GET', '//mydomain.me/somefile');
request.send();

Browser compatibility

• Internet Explorer 6+
• Firefox 3.6.28+
• Chrome 3+
• Opera 12+
• Safari 4+
• iOS Safari 3.2+
• Android 2.1+

(earlier versions of listed browsers will probably work as well)

File sizes

As reported by Closure Compiler:

• Unminified: 13.98KB (3.5KB gzipped)
• Minified: 4.12KB (1.85KB gzipped)

Notes and interesting features

In the spirit of dogfooding, if a browser doesn't support JSON (I'm looking at you, old IE) the library uses itself to load a shim from cloudflare.com's CDN via a JSONPHttpRequest object. Incidentally, this also means that any script can be loaded using JSONPHttpRequest.