Port DataLoader to TypeScript

[NShahri]

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.

[linux-foundation-easycla[bot]]

The committers listed above are authorized under a signed CLA.

• :white_check_mark: login: NShahri / name: Nima Shahri (05c662ae5de37e0b6fc195ad72c3fd45175d8ab7, 1308818e951ae49e84dd30497f9cea5a9307c0fb, 509a35194999f39257cba52568ecc97791feb02d, 523fde1066f6f8e04fdaea3848914c1857b76e4f, 6374f4afa0b7e5fef6d0622846480903ac1f2c67, 910c937b7af659f67fd1d4c1802212e5f09a14f0, 9f967225c2c2ffd608d659809751946511c0faa5, a454ec2b21eaf100caaed02284e51ecb44bb0f91, b0814f924868b883f808ed507925f0b92b610c2a, b73bb0b3e4141f2b1530abb4a73cfc3d5446cedd, da5bfb89300be4bad76ef25c5b3e18a309c405df, ed9862adaad9cc874c60b73cfcde007aa9c1b99c, fab2884b2de1aa2355fd589d6470e3a631036f83, faf3fb08dc6329045d75c92e93fb47db29f4a542, 028d3c9851069cb8f38f528a01335ab070f646cf, 6da3bbbaf647de1d6efbb6e8ff61158262f6698b, 9fc234f60e061f16455e42f271de145b1af9d308, ca45b68aef337e5283489209a10739fe2f9fd896)

[NShahri]

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!

[NShahri]

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

[ardatan]

@NShahri Still failing :/

[productdevbook]

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

[benjie]

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]

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

[benjie]

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

[NShahri]

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

[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: 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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