I'm working on some Javascript that makes use of Firefox 3.5's ability to perform cross-domain XMLHttpRequests… But I'd like to fail gracefully if they aren't supported.
Apart from actually making a cross-domain request, is there any way to detect a browser's support for them?
For future reference, full CORS feature detection should look something like this:
//Detect browser support for CORS
if ('withCredentials' in new XMLHttpRequest()) {
/* supports cross-domain requests */
document.write(CORS supported (XHR));
}
else if(typeof XDomainRequest !== undefined){
//Use IE-specific CORS code with XDR
document.write(CORS supported (XDR));
}else{
//Time to retreat with a fallback or polyfill
document.write(No CORS Support!);
}
You can try this test live using JSBin and see the proper response in IE, Firefox, Chrome, Safari, and Opera.
There are some edge cases in non-browser environments that do support cross-domain XHR but not XHR2/CORS. This test does not account for those situations.
