检测跨域XMLHttpRequests的浏览器支持？

问题描述：

我正在开发一些使用Firefox 3.5的能力来执行跨域XMLHttpRequests的JavaScript。但是如果不支持，我想要优雅地失败。

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.

除了实际发出跨域请求，是否有任何方法可以检测浏览器对它们的支持？

Apart from actually making a cross-domain request, is there any way to detect a browser's support for them?

答

为了将来参考，完整的CORS功能检测应该看起来像这样：

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!");
}

您可以使用JSBin尝试这个测试，并看到在IE，Firefox，Chrome，Safari和Opera正确的响应。

You can try this test live using JSBin and see the proper response in IE, Firefox, Chrome, Safari, and Opera.

在非浏览器环境中有一些边缘情况，确实支持跨域XHR，但不支持XHR2 / CORS。此测试不考虑这些情况。

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.

检测跨域XMLHttpRequests的浏览器支持？

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