Port DataLoader to TypeScript by NShahri · Pull Request #385 · graphql/dataloader

NShahri · 2025-10-30T03:28:39Z

This PR migrates the entire codebase from JavaScript/Flow to TypeScript, modernizing the stack and improving type safety, tooling, and maintainability.

✅ Changes Included

Migrated all source and test files from .js to .ts
Removed Flow types and replaced them with TypeScript equivalents
Added tsconfig.json with strict compiler options
Switched build system from Babel to typescript and node type stripping
Support ESM
Refactored tests to TypeScript with proper type annotations
Updated package.json scripts and dependencies
Upgrade Eslint config
Removed obsolete files
switch to npm

📈 Benefits
This migration lays the foundation for better maintainability, improved tooling support, and enhanced type safety.

…cript and tsup, remove flowbin and babel

…hod as private method in DataLoader

linux-foundation-easycla · 2025-10-30T03:28:47Z

The committers listed above are authorized under a signed CLA.

✅ login: NShahri / name: Nima Shahri (05c662a, 1308818, 509a351, 523fde1, 6374f4a, 910c937, 9f96722, a454ec2, b0814f9, b73bb0b, da5bfb8, ed9862a, fab2884, faf3fb0, 028d3c9, 6da3bbb, 9fc234f, ca45b68)

NShahri · 2025-10-30T09:41:56Z

Hello, @leebyron @saihaj @graphql/dataloader-maintainers. This PR completes a full migration to TypeScript and includes several improvements to the build and test setup. I'd appreciate your review and any suggestions you might have. Thank you!

jgcmarins

Amazing

ardatan

CI seems failing. Could you take a look?

NShahri · 2025-11-03T05:30:57Z

Thanks @ardatan — I’ve fixed the CI issue. Could you please try re-running the workflow when you get a chance?

ardatan · 2025-11-03T09:20:08Z

@NShahri Still failing :/

benjie · 2025-11-03T15:28:36Z

jest.config.ts

+global._onUnhandledRejection = handler => {
+  _.on('unhandledRejection', handler);
+};
+


FAIL src/__tests__/unhandled.test.ts ● Unhandled rejections › Not catching a primed error is an unhandled rejection TypeError: global._onUnhandledRejection is not a function

I think the issue is that this needs to be done in a "jest environment" rather than in the config file; the jest workers don't run with this (unless you have jest -i maybe?) IIRC.

Hi @benjie @ardatan

Unfortunately, it wasn’t possible to add unhandledRejection handler in Jest, even when using custom Jest environments. Because of this limitation, I decided to switch to Vitest.

Additionally, I realized mocking global dependencies like process or setTimeout was difficult since they were required at module import time. To make mocking easier, I refactored the code so that these dependencies are accessed only when the DataLoader is initialized.

Please check the commit and let me know your thoughts.

Still failing unfortunately.

Handling unhandledRejection in jest seems quite tricky— based on my research, it’s nearly impossible to do reliably. The only workaround I found is this approach, but it’s not ideal and feels a bit hacky.

On the other hand, vitest does support handling unhandledRejection, but it requires NodeJs 20+, which might limit compatibility.

Please correct me if I’m mistaken, but it looks like unhandled.test.ts is testing NodeJs behavior rather than application logic. I'm still unsure about the value of testing what happens when a rejected promise isn’t handled by user code. If that’s the case, perhaps this test could be removed or skipped?

Also worth noting: there’s already a test that checks whether the priming error returns a rejected promise, which might be sufficient.

Would it make sense to remove or skip the unhandled.test.ts? Or is there a specific scenario we’re trying to safeguard against that I might be missing?

…asier mocking

productdevbook · 2025-11-08T14:08:39Z

tsup -> tsdown(https://tsdown.dev/) I definitely recommend using this.

benjie · 2025-11-08T15:03:43Z

Wouldn’t it be better to use Node’s type stripping for development, tsc for build, and leave the bundling up to the consumer?

productdevbook · 2025-11-08T15:27:51Z

The reason for the transition. The ecosystem is currently gathered in tsdown.

benjie · 2025-11-09T09:34:00Z

I’m not sure we need to add tsup or tsdown as dependencies. More dependencies, more dependabot alerts 😅

NShahri · 2025-11-12T09:40:26Z

Thanks @benjie @productdevbook
Switched to using Node’s type stripping for development and tsc for the build step.

codecov · 2025-11-12T10:49:41Z

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (a107730) to head (9f96722).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #385   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          164       167    +3     
  Branches        52        55    +3     
=========================================
+ Hits           164       167    +3

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productdevbook · 2025-11-12T11:01:32Z

package.json

-  "module": "dist/index.js",
-  "typings": "dist/index.d.ts",
+  "main": "dist/cjs/index.js",
+  "module": "dist/esm/index.js",


"main": "dist/index.js",
"module": "dist/index.mjs",

Can we extract this as mjs?

Hi @productdevbook

Unfortunately, TypeScript doesn’t provide a built-in way to enforce specific file extensions, so implemented a custom postbuild script to handle that.

This is one of the advantages of using a tool like tsdown, as it abstracts these details and simplifies the build process.

main and module are outdated in favor of exports ("package entry points") which wouldn't require a postbuild step.

NShahri and others added 10 commits October 28, 2025 23:48

upgrade packages including eslint, jest and changesets, install types…

b0814f9

…cript and tsup, remove flowbin and babel

use tsup to build/watch the package

910c937

fix the eslint config and script

a454ec2

fix prettier config

fab2884

fix the jest config and enaable ESM for jest

ed9862a

mirate to typescript

faf3fb0

remove not required files like flow,jest,yarn and babel configs

b73bb0b

refactor: make DataLoader properties private and define move some met…

05c662a

…hod as private method in DataLoader

Implement custom handler for unhandled promise rejections in Jest tests

6da3bbb

Switch from Yarn to NPM for dependency installation

028d3c9

Update validation workflow name and trigger events

9fc234f

jgcmarins approved these changes Oct 31, 2025

View reviewed changes

NShahri mentioned this pull request Nov 1, 2025

[REQUEST] ESM version of Dataloader #379

Open

ardatan requested a review from saihaj November 3, 2025 00:22

ardatan approved these changes Nov 3, 2025

View reviewed changes

ardatan requested changes Nov 3, 2025

View reviewed changes

Fix command syntax for running CI tests in validation.yml

ca45b68

NShahri requested a review from ardatan November 3, 2025 05:27

benjie reviewed Nov 3, 2025

View reviewed changes

NShahri added 2 commits November 5, 2025 14:20

use global dependency when DataLoader initiated, refactor tests for e…

6374f4a

…asier mocking

skip unhandled rejections test

509a351

NShahri force-pushed the typescript branch from 14fbbef to 509a351 Compare November 5, 2025 01:26

NShahri added 2 commits November 12, 2025 21:34

replace tsup with tsdown

523fde1

use Node’s type stripping for development, tsc for build

da5bfb8

update package.json to correct paths for module exports, cleanup

1308818

productdevbook reviewed Nov 12, 2025

View reviewed changes

change the output file structure and extension

9f96722

NShahri force-pushed the typescript branch from 4f4d7dc to 9f96722 Compare November 14, 2025 04:08

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