feat(repo): migrate build system to tsdown for proper ESM/CJS support

[mandarini]

Summary

This PR migrates the build system for postgrest-js, storage-js, and supabase-js from the legacy tsc + wrapper.mjs approach to tsdown, fixing critical ESM module resolution issues that caused production outages for users.

Background

I initially planned to use tsup, but discovered it's no longer actively maintained. The tsup repository itself recommends using tsdown (its actively maintained successor built on Rolldown).

Issues Fixed

Issue	Description	Root Cause
#1955	AuthClient is null - jsdelivr CDN imports broken	wrapper.mjs incompatible with jsdelivr's /+esm transform
#1942	exports is not defined - Vite dev regression	wrapper.mjs imports CJS, crashes in browser ESM context
#1880	ERR_MODULE_NOT_FOUND - Nuxt environment broken	Missing .js extensions in ESM imports

All three issues stem from PR #1914 which introduced wrapper.mjs as a workaround. This PR properly fixes the underlying issue.

What Changed

Build Output Structure

Before:

  dist/
  ├── main/index.js          # CJS
  ├── module/index.js        # ESM (missing extensions)
  ├── esm/wrapper.mjs        # ESM wrapper → imports CJS (broken)
  └── umd/supabase.js        # UMD (webpack)

After:

  dist/
  ├── index.cjs              # CJS
  ├── index.mjs              # ESM (proper, self-contained)
  ├── index.d.cts            # CJS types
  ├── index.d.mts            # ESM types
  └── umd/supabase.js        # IIFE (tsdown)

Package Exports

Before:

  {
    "main": "dist/main/index.js",
    "module": "dist/esm/wrapper.mjs",
    "types": "dist/module/index.d.ts",
    "exports": {
      ".": {
        "types": "./dist/module/index.d.ts",
        "import": "./dist/esm/wrapper.mjs",
        "require": "./dist/main/index.js"
      }
    }
  }

After:

  {
    "main": "dist/index.cjs",
    "module": "dist/index.mjs",
    "types": "dist/index.d.cts",
    "exports": {
      ".": {
        "import": {
          "types": "./dist/index.d.mts",
          "default": "./dist/index.mjs"
        },
        "require": {
          "types": "./dist/index.d.cts",
          "default": "./dist/index.cjs"
        }
      },
      "./dist/*": "./dist/*",
      "./package.json": "./package.json"
    }
  }

Files Changed

Removed (no longer needed)

• wrapper.mjs files (postgrest-js, supabase-js)
• scripts/copy-wrapper.cjs files
• scripts/fix-esm-extensions.cjs
• webpack.config.js files (storage-js, supabase-js)
• tsconfig.module.json files

Added

• tsdown.config.ts for postgrest-js, storage-js, supabase-js
• test/module-resolution.test.mjs - ESM import tests
• test/module-resolution.test.cjs - CJS require tests
• Module resolution CI job with attw validation

New Tests

To prevent regression, this PR adds comprehensive module resolution tests:

Test	Purpose
test:exports	Validates package exports with attw
test:esm	Tests ESM imports work, explicitly checks AuthClient is not null
test:cjs	Tests CJS requires work
UMD test (extended)	Verifies all clients (auth, storage, functions, postgrest, realtime) are bundled

CI now runs a dedicated module-resolution job that validates:

• Package exports work for node10, node16-cjs, node16-esm, and bundler resolution
• ESM imports resolve correctly with all clients accessible
• CJS requires work correctly

Backward Compatibility

• ./dist/* wildcard export maintained for deep imports
• UMD bundle path unchanged (dist/umd/supabase.js)
• All public APIs unchanged

Related:

• fix(supabase): resolve jsDelivr CDN ESM import failure #1950
• fix(supabase): resolve jsDelivr CDN ESM import failure with .js extensions #1953
• fix(supabase): add esm wrapper to resolve module not found error in nuxt #1914
• Module import/export mismatch #1955
• Vite dev regression after #1914: exports is not defined from CJS wrapper in @supabase/supabase-js@^2.86.0 #1942
• ^2.82.0: "Cannot find module" error in Nuxt environment (2.83, 2.84) #1880

[pkg-pr-new]

Open in StackBlitz

@supabase/auth-js

npm i https://pkg.pr.new/@supabase/auth-js@1961

@supabase/functions-js

npm i https://pkg.pr.new/@supabase/functions-js@1961

@supabase/postgrest-js

npm i https://pkg.pr.new/@supabase/postgrest-js@1961

@supabase/realtime-js

npm i https://pkg.pr.new/@supabase/realtime-js@1961

@supabase/storage-js

npm i https://pkg.pr.new/@supabase/storage-js@1961

@supabase/supabase-js

npm i https://pkg.pr.new/@supabase/supabase-js@1961

commit: 97872e7

[coveralls]

coverage: 80.896% (-0.5%) from 81.37%
when pulling 97872e7 on feat/use-tsup
into f346169 on master.