Better error message when xhr onerror

i just found xhr onerror always reject error with same message, it’s very hard to find error cause.

xhr.onerror = function() {
    reject(new TypeError('Network request failed'))
}

VS

[adamvoss]

I have done some exploration of this. The conclusion I came to is there is no consistent way to provide more information. On some platforms, more information is available so an implementation that provides more information would just to code for various cases. Granted my exploration was against browsers that have a native fetch implementation so there would exist a very slight chance that the places that need polyfill do all behave in the same manner.

To summarize:

Firefox (49.0): The passed parameter is an Exception. The relevant information is on the name member. Chromimum (53.0.2785.143): The passed parameter is a ProgressEvent. The closest thing to relevant information says “error.” The XMLHttpRequest is accessible via the ProgressEvent but responseText is an empty string. The developer console does contain an error containing relevant information, but that is outside of the executing JavaScript. NativeScript (2.3.0): The passed parameter is some kind of Error. The relevant information is on the message member. React Native (inferred from @lloydsheng’s comments): Unknown if a parameter is passed but you can access the XMLHttpRequest via closure. Relevant information is on the responseText member.

According to the documentation for Internet Explorer 8, there are no parameter passed to the event handler, which near as I can tell matches the spec. However, implementation may differ from documentation.

[lloydsheng]

@bergr01 The second error message was from iOS network framework. because the latest react native direct reference the fetch package. and i found this message available retrieval from xhr.responseText