jquery/jquery — comment on commit cc4a999648d2623972e6dabad0e6c4b1bb60458a
File:  line 0
By jaubourg:

Well, it's not actually expecting a string here, because it's catching around the use of converters (where native exceptions can be thrown depending on how such or such converter is implemented). The third parameter of the error callbacks (which is the sole use of the error variable here) is supposed to be the original exception whenever available. In fact same goes for transports actually.