SourceCache checks status 404 but status code not sent in postMessage

[deanm]

When one of the web workers makes an AJAX request that fails, it will throw an AJAXError (with status: Number) back to the callback. Ex:

mapbox-gl-js/src/source/vector_tile_source.js

Line 107 in 25e5f1d

tile.workerID = this.dispatcher.send('loadTile', params, done.bind(this));

However, when this goes through the actor, this AJAXError is simply converted to a string for the message posted back to the main thread:

mapbox-gl-js/src/util/actor.js

Line 68 in 25e5f1d

error: err ? String(err) : null,

It looks like _tileLoaded however is specifically trying to handle the condition for 404:

mapbox-gl-js/src/source/source_cache.js

Line 228 in 25e5f1d

if (err) {

However the err object will have just been a generic Error recreated from the string:

mapbox-gl-js/src/util/actor.js

Line 77 in 25e5f1d

callback(new Error(data.error));

So it seems like there is some logic to handle 404 errors specially, however as the network fetches are usually done by the source workers, the status code doesn't make it back to that code.

[mollymerp]

fixed in #6126