Why do we default to `allowJs: true`?

[chriskrycho]

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Why do we need allowJs? I've had issues with TS errors being ignored until publish time (and breaking publishing automation) because allowJs is explicitly set to false by ts:precompile here

https://github.com/typed-ember/ember-cli-typescript/blob/v3.1.3/ts/lib/commands/precompile.ts#L31

_Originally posted by @rwjblue in https://github.com/render_node/MDIzOlB1bGxSZXF1ZXN0UmV2aWV3VGhyZWFkMjY0OTQzOTgzOnYy/pull_request_review_threads/discussion

(I plan to dig into this next week; I just wanted to leave this here so I don't forget!)

[rwjblue]

For reference, the case where the failure only happened upon running ts:precompile was over in @ember/test-helpers.

Over there we run tsc --noEmit in CI (along with other linting commands) to attempt to ensure that we don't introduce TypeScript issues for each pull request.

The issue was introduced in https://github.com/emberjs/ember-test-helpers/pull/819. CI passed there (including a tsc -p tsconfig.json --noEmit) as you can see here. However, when I attempted to publish the next version I got an error from ember ts:precompile which was essentially an issue saying that requirejs was not a thing (it was used here). I fixed it over in https://github.com/emberjs/ember-test-helpers/pull/849.

[jamescdavis]

I hit this last week in an engine for work where, being new to the codebase, I didn't realize allowJs: true was set and it didn't bite me until publish time. I'm in favor of allowJs: false by default.

[dfreeman]

I'd love to revisit our whole default tsconfig.json prior to the 4.0 release if we can.

[chriskrycho]

We've revisited our tsconfig.json and its source of truth also now lives at @tsconfig/ember. 🎉