So I ran into this problem with (version 3.9) esri/arcgis/utils#createMap where my defined basemap layer is down, so the map creation errors out completely and breaks my app.
What I can do is use the error function to add a different basemapLayer url (like the Esri World Imagery), but there are a few issues here.
Error seems to delete basemap object from basemapLayers array: This means I have to add a new object instead of just change the URL. It would be cool if you didn't mutate my objects.
Error only tells me a URL is not valid: This could mean it's a basemapLayer or maybe an operationalLayer (map fails to create with a bad op layer URL too, checked), I'm not sure how to tell. This makes error handling these kind of things more difficult.
Map creation doesn't need to be halted because of a bad URL: A map can exist without a basemap, maybe add the errors to the response callback to check for any errors that occured during the map creation process.
In this case, I can tell after the fact that the basemapLayer is dead, but this doesn't help me in production to handle these errors if I can't tell what has gone wrong. The Error codes do contain an empty details array, so maybe the JS API internals could populate that with some more useful information.
Although I like the idea of not breaking map creation because of a bad URL to begin with. It's much easier to handle a missing layer inside the application than it is to decipher what went wrong in the map creation process.
*edit* - I just double-checked. The response object from the createMap promise does have an errors array. Can you just put any map creation errors there, including invalid URL errors? I suppose I'm confused why a broken basemap/operational URL will halt the map creation process.
I agree. I'm frustrated that I can catch the error and load a backup base map, but I can't keep the original error from propagating, causing the map loading process to halt.
I want to set up a failover process for the base map so that my users will see some type of map underneath my data, instead of just a blank background.
