Document File name has a '.js' extension - stripping it

TypeScript Version: 4.2.0-dev.20201211

Search Terms: typescript File name has a '.js' extension - stripping it

Code

https://github.com/sguillia/ts-repro-III

other.ts

import * as index from "./index.js"

index.ts

export { }

Compile with:

tsc other.ts --traceResolution

Expected behavior:

Does not compile?

Actual behavior:

$ tsc other.ts --traceResolution
...
File name '/path/to/ts-repro-III/index.js' has a '.js' extension - stripping it.
...

This document is very good:
https://www.typescriptlang.org/docs/handbook/module-resolution.html

But it doesn't talk about resolution of modules with their extensions.

The actual behavior is fine but I did not manage to find its documentation

Same issue for jsx

$ tsc other.ts --traceResolution
...
File name '/path/to/ts-repro-III/index.jsx' has a '.jsx' extension - stripping it.
...

Would it be possible to document

• which extension are trimmed?
• what look-ups are performed based on the file name with extension stripped?

Playground Link: https://github.com/sguillia/ts-repro-III

Related Issues: no

Start with the module-resolution handbook page linked in the issue and compare its current explanation with the traceResolution output for the .js and .jsx examples. Document which extensions are stripped and which lookups follow, then verify that the page answers both questions without changing the compiler behavior.