#89 improved for compatibility

[naugtur]

Merged #89 and added a way to distinguish timeout errors without parsing messages.
error.code is compatible with what https://github.com/request/request does

[mattdesl]

One more thing that might be nice is an error code for 'abort()'. Right now it's tricky to know whether the error was due to cancellation or something more serious.

It could be the same code used by 'http' abort()

[naugtur]

xhr only ever calls abort() when our manual timeout occurs, so the code is ETIMEDOUT;
we don't expose our own abort method to proxy the original one

Or did I misunderstand?

[heff]

@dmlap any feedback?

Looks good to me, thanks @naugtur!

[mattdesl]

@naugtur In all browsers, the following should be supported:

var req = xhr(url, (err, resp) => {
   // err will be "Internal XMLHttpRequest Error"
})

// when user cancels request
cancelButton.on('click', () => req.abort())

However, it's hard to distinguish between a cancel or another time of error.

I can open another issue if it's outside the scope of this fix.

[naugtur]

@mattdesl It's not related to this issue imho. Feel free to add a new issue for that. (although I don't see how it'd be possible for xhr to know that someone aborted the request; if you aborted it, you know you did)

[dmlap]

@naugtur this looks perfect. Thank you!