tsx REPL does not respect NODE_REPL_MODE environment variable or --use_strict CLI flag at transpile time

[jhmaster2000]

Acknowledgements

• I searched existing issues before opening this one to avoid duplicates
• I understand this is not a place for seek help, but to report a bug
• I understand that the bug must be proven first with a minimal reproduction
• I will be polite, respectful, and considerate of people's time and effort

Minimal reproduction URL

N/A

Version

v4.7.1

Node.js version

v20.10.0

Package manager

N/A

Operating system

Windows

Problem & Expected behavior

Put simply, tsx has the same issue I myself reported to deno a while back here: denoland/deno#13775

But I'll re-explain it here anyway just in case.

Node.js supports the NODE_REPL_MODE flag documented here or the --use_strict CLI flag (seemingly undocumented at the time?) to configure the REPL to run in strict mode instead of the default sloppy mode, you can test this with:

1. Make sure NODE_REPL_MODE is unset to not interfere with the reproduction
2. node -> 01 -> Returns 1
3. Exit the REPL
4. node --use_strict -> 01 -> Strict mode error (expected)

Reproducing the same steps above but with tsx in place of node results in step 4 still returning 1 instead of the expected error. Notice however the following alternative reproduction:

1. Make sure NODE_REPL_MODE is unset to not interfere with the reproduction
2. tsx -> eval('01') -> Returns 1
3. Exit the REPL
4. tsx --use_strict -> eval('01') -> Strict mode error (expected, it works now!)

Note: Both reproductions can also be done through the environment variable instead of the flag with identical results.

The conclusion here is that the runtime itself is respecting the options and running in strict mode, after all it is just regular Node.js in the end, but tsx is not running transpilation in strict mode in accordance to these REPL flags, so it transpiles these strict-mode-invalid literals into "resolved" literals that are valid in strict mode, causing unintended odd looking behavior.

Contributions

• I plan to open a pull request for this issue
• I plan to make a financial contribution to this project