Bloomberg feedback on TypeScript 4.6 Beta

This issue has been created by the team responsible for the infrastructure behind most of Bloomberg’s TypeScript code.

Summary

We have tested TypeScript 4.6.0-beta on our codebase and our experimentation has not revealed any new errors in TypeScript source, pointing to this being a straightforward update.

Grammar Errors in JavaScript Files

As reported in the 4.6 iteration plan, TypeScript now reports grammar errors for JavaScript files contained within TypeScript projects: https://github.com/microsoft/TypeScript/issues/45349

These errors are now reported even when checkJs is not specified, and require explicit checkJs: false to disable them:

Before:

• checkJs false or <unspecified>: no diagnostics on *.js files
• checkJs true: grammar + inference-based type errors on *.js files

After:

• checkJs false: no diagnostics on *.js files
• checkJs <unspecified>: grammar errors on *.js files
• checkJs true: grammar + inference-based type errors on *.js files

Is it intentional that users now need to be explicit to avoid any errors on *.js files?

Credits to @dragomirtitian & @tchetwin for helping with this investigation.

[sandersn]

@molisani It would help me to talk to you to decide whether Bloomberg’s errors will appear in most other codebases and whether to turn off that error. I sent you a DM on twitter in case you have time in the next couple of days.

[sandersn]

From talking in person, it sounds like the mismatch between the new errors and the runtime should only apply to Bloomberg, and the few other people who are using that (quite old) runtime.