ERR_MODULE_NOT_FOUND: add a property to exception object to hold failing import's argument

[rulatir]

Is your feature request related to a problem? Please describe.

I am developing a framework that uses node as a host for user scripts. The framework loads them dynamically with the async import() function, and the userscripts can also import other modules with import statement.

When I call that import() function, I basically want to rethrow all errors thrown by it, except for one very specific condition: when the import() function fails with ERR_MODULE_NOT_FOUND because the userscript file itself wasn't present in the location just tried. The userscript might still be found in some other search path, which is why its absence in any given candidate location is not an error. If however the import() function failed with ERR_MODULE_NOT_FOUND because some other module imported by the userscript was not found, then I want to rethrow that error.

Describe the solution you'd like

Add a property to the exception object thrown for ERR_MODULE_NOT_FOUND that will hold the exact value of the argument that was given to the failing import function or statement.

Describe alternatives you've considered

I considered checking for existence first and then attempting to import(), but that is a known antipattern.

I considered parsing the message or stack property, but that would be a hack. These properties are probably locale dependent and their format is not set in stone.

I looked into custom loaders and found the subject difficult, scary, apparently indefinitely experimental, and an overkill for this particular purpose. I need a simple and reliable way.

[DerekNonGeneric]

Thanks for raising this — the request sounds reasonable.

Hope to take a deeper look a bit later. Curious what others may think on the matter.

/cc @nodejs/modules

[ljharb]

A custom loader doesn't sound like overkill at all to me - it's precisely what you're trying to achieve. The other adjectives, however, are likely true at this time.

[github-actions]

There has been no activity on this feature request for 5 months and it is unlikely to be implemented. It will be closed 6 months after the last non-automated comment.

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[rulatir]

@DerekNonGeneric is it "a bit later" yet? ;)

[GeoffreyBooth]

Doesn’t the error message included with ERR_MODULE_NOT_FOUND have the file path you’re asking for? Yes it’s inside an English sentence that you’d need to parse out, but even if the message itself changes in the future, code like error.description.includes(fullPathToUserScript) would work as long as the path to the missing module never gets removed (which is very unlikely). Seeing as your use case is very specific, I don’t know if it’s likely that Node will add this path as its own property on the error object.