ESM Module Identity

[marklundin]

Reporting this here from Discord

Essentially, a module is preloaded with the query string /module.js?id=123. If this is then later imported via user code, it's generally imported explicitly without the id param, ie import "module.js". This creates a new module identity, meaning /module.js?id=123 resolves as an entirely new module. This can cause problems modules containing side-effects.

When a module is preloaded, it should not create a new module identity.

See repro here https://playcanvas.com/project/1280764/overview/import-test

[Maksims]

As I understand there is already pre-processing of script happens? If so, appending id/hash - would be a sufficient path. As it would avoid a need of changing the caching logic for code.
Are import maps used?

[marklundin]

Yep there is a pre-processing of scripts happening in a SW which maps module.js => module.js?id=123, however this was only being applied to requests originating from user scripts, ie. an explicit import X from module.js. The initial preload step would still load directly from module.js?id=123, meaning from the browsers perspective, these are 2 different url's.

I've submitted a patch which ensures the preload uses the same path as any explicit import paths within scripts.