map.onError is not helpful by default

[scothis]

The error message logged by the default onError handler within Map is often blank, and completely unhelpful.

https://github.com/mapbox/mapbox-gl-js/blob/v0.11.0/js/ui/map.js#L788

[jfirebaugh]

This is likely specific to a certain type of error. This is what I see for a style validation failure, for example:

What do you see after clicking the disclosure triangle? Can you track down the source of this by other means?

[scothis]

Seems to be triggered by a tile 404ing

[scothis]

Also, seeing a user report of tile 404s blocking the map load event.

laurenancona/philly-pope-map@9dce95a

[scothis]

Since we expect to receive a 404 for empty tiles, treating the response as an error seems wrong.

[mjumbewu]

Yup, the error comes from the 'load-tile' worker process. It treats 404s the same as any other error. The fix/hack we used is mjumbewu@b058bdf, but I'm pretty sure that's not entirely reliable. Maybe https://github.com/mapbox/mapbox-gl-js/blob/6c59629/js/util/ajax.js#L48 should check for 404 and return a special type of error (or no error).

[lucaswoj]

fixed in #1799