Use Awaited type to avoid Promise<Promise<T>>

[urbanfly]

When debouncing a Promise-returning function, the returned function has a type of Promise<Promise<T>> which is not accurate - see microsoft/TypeScript#27711

In TypeScript 4.5, a new Awaited<T> type was introduced to solve this problem.

• docs
• release notes

This PR simply wraps the ReturnType<F> with Awaited<...> in order to get an accurate return type for the created function.

Several packages were updated:

• Typescript bumped to 4.5 in order to access this type
• microbundle in order to build
• jest / ts-jest in order to test with this type
• tsd in order to validate the types

[chodorowicz]

Hey @urbanfly
Sorry for the absurdly long delay with replying 🙇

The change makes sense, thanks. There's one issue though, the type for the callback functions Options<Awaited<ReturnType<F>>> doesn't match the existing behavior as the promises there are not flattened with resolve and result is passed directly to the callback function. I've added tests that document that behavior → https://github.com/chodorowicz/ts-debounce/pull/70/changes

if you're still around and interested in merging this change, I'm happy to do it after this issue is fixed.

[urbanfly]

I didn't originally get your point about the callback/options. I have removed Awaited from the options argument.

[chodorowicz]

Thanks, looks good!

There's conflict with the base branch, which needs to get resolved first (both merge and rebase are fine)
Also, type test have issue

  ✖  34:0  Parameter type () => Promise<number> is declared too wide for argument type DebouncedFunction<[], () => Promise<number>>.

expectType requires strict type equality. using expectAssignable from tsd should be good to solve the problem.

Happy to merge this after resolving this two issue.

[urbanfly]

I've rebased and tried to run the tests. The Jest tests pass, but test:types fails on tsd:

The type definition dist/src/index.d.ts does not exist at /workspaces/ts-debounce/dist/src/index.d.ts. Is the path correct? Create one and try again.

It seems like it depends on the build script to run first, but that also fails:

Add @babel/preset-flow to the presets section of your Babel config to enable transformation.
If you want to leave it as-is, add @babel/plugin-syntax-flow to the 'plugins' section to enable parsing.

If you already added the plugin for this syntax to your config, it's possible that your config isn't being loaded.
You can re-run Babel with the BABEL_SHOW_CONFIG_FOR environment variable to show the loaded configuration:

npx cross-env BABEL_SHOW_CONFIG_FOR=/workspaces/ts-debounce/src/index.ts <your build command>

See https://babeljs.io/docs/configuration#print-effective-configs for more info.

I was able to work-around it locally by removing the --noEmit flag from tsc so that the dist folder gets populated (and then adjust the paths for types in package.json to match the expectation). So at this point, npm run test passes, but only with some uncommitted work-arounds.

[Copilot]

Pull request overview

This PR improves the TypeScript typings for debounce so that debouncing a Promise-returning function yields Promise<T> instead of Promise<Promise<T>>, leveraging TypeScript 4.5’s Awaited<T> utility type.

Changes:

• Update DebouncedFunction/internal Promise generics to use Awaited<ReturnType<F>> for the debounced return type.
• Add a tsd assertion to ensure the debounced function type is assignable to () => Promise<number> for async functions.
• Bump tooling dependencies (TypeScript, Jest, ts-jest, microbundle, tsd) to versions compatible with Awaited.

Reviewed changes

Copilot reviewed 3 out of 5 changed files in this pull request and generated 3 comments.

File	Description
src/index.ts	Uses Awaited<ReturnType<F>> to prevent Promise<Promise<T>> in debounced return types.
src/index.test-d.ts	Adds type-level assertions verifying the debounced return type is a single Promise.
package.json	Updates dev tooling versions to support Awaited and related build/test tooling.

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[chodorowicz]

The CI job, which includes pnpm run test:types, is green.

The last thing is to remove package-lock.json from the PR, as this project uses pnpm and pnpm-lock.yaml.

[urbanfly]

I don't know how I "Started a review". I just replied to Copilots's comment re: @types/jest version within VS Code.

[urbanfly]

I saw the build failure and have now properly installed @types/jest to v29 so that the pnpm-lock.json file is updated correctly.

Updating to Jest v29 made useFakeTimes("modern") fail, so removed the parameter. See https://jest-archive-august-2023.netlify.app/docs/28.x/upgrading-to-jest28/#jestusefaketimers

[chodorowicz]

@all-contributors add @urbanfly for code

[allcontributors]

@chodorowicz

I've put up a pull request to add @urbanfly! 🎉

[chodorowicz]

Thanks for your contribution @urbanfly 🙇