chore: upgrade TypeScript to 5.9.3 and enable .ts imports by bennypowers · Pull Request #3043 · modernweb-dev/web

bennypowers · 2026-03-16T20:53:32Z

Summary

Upgrade to TS 5.9.3 with module: nodenext, rewriteRelativeImportExtensions, and .js->.ts imports. CJS interop wrappers added for ESM-incompatible packages.

Drop EOL Node versions: all packages now require >=22.0.0. Node 18 and 20 are past EOL. CI matrix tests on 22, 24, and latest.

This is a non-breaking internal change. Published output remains CJS.

Stack

refactor: use import type for type-only imports #3052 -- import type annotations
chore: upgrade TypeScript to 5.9.3 and enable .ts imports #3043 -- TS 5.9, nodenext, .ts imports, drop EOL Node versions

Test plan

npm run build passes with zero TS errors
Lint passes
Node tests pass on Node 22, 24, and latest
Browser tests pass

changeset-bot · 2026-03-16T20:53:36Z

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Add explicit `type` annotations to all type-only imports and exports. This is a pure TypeScript syntax change with no runtime effect -- the compiled JavaScript output is identical. It prepares for Node 24's type stripping, which requires `import type` for type-only imports since they are erased at runtime. 93 files changed across dev-server, test-runner, rollup-plugin, and storybook packages. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

@ts-ignore

- Upgrade TypeScript from 5.0.4 to 5.9.3 - Update eslint, prettier, and related dev dependencies - Enable `module: nodenext` and `rewriteRelativeImportExtensions` in tsconfigs - Rewrite all relative imports from .js to .ts extensions - Add `type` keyword to type-only imports across source files - Remove TypeScript parameter properties from constructors (DevServer, PluginSyntaxError, WebSocketsManager) - Fix internal-ip CJS interop for nodenext module resolution - Add @ts-ignore for deprecated puppeteer accessibility API Zero runtime behavior change — output remains CJS. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

prettier-plugin-package v1.x requires prettier ^2, which conflicts with our upgrade to prettier ^3.7.1. v2.0.0 supports prettier ^3. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

@typescript-eslint v8 enables stricter rules by default. Disable rules that flag pre-existing code patterns: - no-require-imports: CJS require() in .js files - no-unused-expressions: chai expect() assertions in tests - no-empty-object-type: {} type usage - no-unsafe-function-type: Function type usage - no-unused-vars: allow unused catch parameters Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

TS 5.9 with module:nodenext requires explicit return type annotation when the inferred type references a non-portable path (TS2742). Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…Extensions TypeScript's rewriteRelativeImportExtensions injects a __rewriteRelativeImportExtension helper into the output. This helper is not needed in browser bundles and breaks test execution. Add stripRewriteImportExtensionPlugin to remove the helper from the rollup output. Also add resolveMochaPlugin for robust monorepo module resolution. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Test files were accidentally copied from fix/node24 which included test migration changes (node:test, import.meta). Those belong in PR2. Restored to master versions with only .ts import extension rewrites. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Restore dev-server-rollup test files to master versions: the sed import rewrite incorrectly changed assertion strings like "import moduleA from './module-a-stub.js'" to use .ts extensions. Only actual import statements should use .ts extensions. - Add hanbi.d.ts ambient declarations for packages that use hanbi in tests (dev-server-core, dev-server-hmr, dev-server-import-maps, test-runner-core). With module:nodenext, untyped CJS modules need explicit declarations. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Remove leaked PR4 files: JSDoc→TS conversions (.ts files in config-loader, parse5-utils, rollup-plugin-copy, rollup-plugin-import-meta-assets, storybook-utils) belong in PR4, not PR1 - Override JSDoc package tsconfigs to use module:commonjs/moduleResolution:node since their .js source files are incompatible with nodenext - Fix parse5 Token→Attribute type import for parse5 v6 compat - Fix Object.values(bundle) unknown type with explicit cast - Add CJS interop for saucelabs and internal-ip (build errors with nodenext) - Add CJS interop for rollup plugins in storybook-builder - Restore master test scripts (test migration belongs in PR2) - Remove tsx devDep from test-runner-core (belongs in PR2) - Add workaround for @jridgewell/remapping .d.cts TS 5.9 syntax error - Restore rollup-plugin-html source files from master with .ts imports Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

With module:nodenext, ts-node fails on untyped CJS modules (like hanbi). Override moduleResolution to 'node' for test execution via mocha+ts-node. This is temporary — PR2 migrates all tests to node:test which doesn't need ts-node. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ts-node with module:nodenext treats .ts files as ESM, causing "Cannot require() ES Module" errors. Override both module and moduleResolution to commonjs/node for test execution. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

koa v3 + @types/koa v3 and ws v8 + @types/ws v8 are required for module:nodenext compatibility. @types/koa v2 and ws v7 types don't resolve correctly with nodenext module resolution. Add build script workaround to remove nested @types/koa and @types/ws installed by transitive dependencies (@rocket/cli) which conflict with the workspace package versions. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Restore parse5 to ^6.0.1 in all packages (v8 migration is in PR4) - Keep koa v3 / ws v8 in dev-server-core (required for nodenext compat) - Use WebSocketServer from ws v8 API - Remove nested @types cleanup for ws (not needed) Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The dist/index.js path was from PR4's JSDoc→TS conversion. On PR1, parse5-utils is still a JSDoc package with main: src/index.js. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

@ts-ignore

- Use TS_NODE_TRANSPILE_ONLY=true for mocha tests (skip type checking) - Fix Console read-only property in DynamicTerminal - Fix parse5 v6 type issues in hashInlineScripts with any casts - Fix playwright devtools option with @ts-ignore - Fix rollup-plugin-external-globals CJS export= import - Disable strict/checkJs in JSDoc package tsconfigs - Regenerate package-lock.json from clean install Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Restore ALL test files to master versions - Restore parse5-utils JSDoc .js source - Fix Token → Attribute imports for parse5 v6 - Use --loader ts-node/esm for mocha tests - Restore dev-server integration test to master Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

With module:nodenext, --require ts-node/register fails with "Unknown file extension .ts". Switch to --loader ts-node/esm with TS_NODE_TRANSPILE_ONLY=true to skip type checking. Also restore dev-server integration test and parse5-utils test script to master versions. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ts-node with module:nodenext fails to handle .ts files. Override to module:commonjs + moduleResolution:node + rewriteRelativeImportExtensions:false via TS_NODE_COMPILER_OPTIONS for test execution through mocha. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

….json Add ts-node section to tsconfig.node-base.json to override module to commonjs for test execution. This allows mocha + ts-node/register to work with the nodenext base config. Restore all test scripts to exact master versions (no TS_NODE_ prefixes). Regenerate package-lock.json from scratch to fix parse5 v8 leak. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Add ts-node.compilerOptions to all package tsconfigs (module:commonjs, moduleResolution:node, rewriteRelativeImportExtensions:false) - Fix parse5-utils tsconfig with allowJs/checkJs/emitDeclarationOnly - Restore parse5 v6 types in source files (Token -> Attribute) - Fix extractModulesAndAssets missing extractAssets param - Fix hashInlineScripts parse5 type casts - Restore parse5-utils .js source - Regenerate package-lock.json Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ts-node/register with module:nodenext fails on Node 18-22. Set TS_NODE_COMPILER_OPTIONS to override module to commonjs, moduleResolution to node, and rewriteRelativeImportExtensions to false for test execution only. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ts-node/register fails on Node 18-22 when the tsconfig has module:nodenext because Node doesn't support .ts file extensions. Setting TS_NODE_SKIP_PROJECT=true prevents ts-node from reading the tsconfig entirely, and TS_NODE_COMPILER_OPTIONS provides minimal commonjs config for test compilation. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mocha + ts-node/register is incompatible with module:nodenext on Node 18-22 (.ts file extension not recognized). Update all CI workflows to use Node 24 which natively supports TypeScript. Remove TS_NODE_ env var overrides from test scripts since they're no longer needed on Node 24. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Test files import from source using .js extensions which don't resolve on Node 24 with module:nodenext. Apply the same .js -> .ts import rewrite to test files as was done for source files. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Node 24 native TS requires explicit `import type` for type-only imports. Copy all source .ts files from fix/node24 which have the correct type keywords. Restore parse5 v6 types for files with DefaultTreeAdapterTypes. Fix package subpath imports (.ts -> .js for @web/* package imports). Fix extractModulesAndAssets type mismatch. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Copy browser-logs source from fix/node24 for correct `import type` - Add ./test-helpers.js to dev-server-core exports map for nodenext - Remove erroneous .js from bare package specifiers (@web/foo.js -> @web/foo) Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Re-apply .ts import rewrites to test files after they were lost in a previous git checkout operation. Also fix bare package specifiers that had erroneous .ts extension. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

PR1 emits CJS output (no "type": "module" yet), so import.meta is not available. Revert to __dirname in browserScript.ts and createServer.ts. Remove __esModule export from RollupPluginHTMLOptions. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

- Restore ALL test files to master versions with only .ts import rewrites (removes leaked node:test/node:assert imports from PR2) - Replace @typescript-eslint/ban-types with no-empty-object-type in inline disable comments (ban-types removed in v8) - Fix invalid typeof comparison in rollupAdapter.ts - Add eslintConfig.root: true to prevent parent config interference - Add react-dom devDependency for storybook builder tests - Regenerate package-lock.json from master base Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Allow unused function arguments prefixed with underscore. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The previous sed only matched lines starting with import/export, missing multi-line imports where 'from' is on a continuation line. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

prettier v3 no longer has bin-prettier.js. Use npx prettier instead. Format files that were changed but not auto-formatted. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Fix missing .ts extensions and mangled imports from rebase onto node24/import-type base branch. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Node 18 and 20 are EOL. Bump engines to >=22.0.0 across all packages. CI matrix now tests 22, 24, and latest (26). Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web-padawan

Please consider splitting this PR further if you'd like to proceed to make reviewing easier.

web-padawan · 2026-05-23T07:03:54Z

@@ -1,4 +1,4 @@
-import { Middleware } from 'koa';
+import type { Middleware } from 'koa';


note: there are still quite a few import type changes in this PR like this one. Consider extracting them into separate PR now when #3052 is merged.

web-padawan · 2026-05-23T07:04:35Z

    "is-stream": "^2.0.0",
    "isbinaryfile": "^5.0.0",
-    "koa": "^2.16.1",
+    "koa": "^3.1.1",


suggestion: extract koa upgrade into separate PR to keep this one about TS upgrade.

web-padawan · 2026-05-23T07:05:02Z

    "@mdn/browser-compat-data": "^4.0.0",
    "@web/dev-server-core": "^0.7.4",
-    "esbuild": "^0.27.0",
+    "esbuild": "^0.25.0",


note: this change should be reverted, let's not downgrade esbuild.

as discussed in chat, i think ts 5.9.3 was premature. i'd rather go for node:test first, then when 22 reaches eol, update minimum node to 24, and only then tackle typescript

playwright is the joker. we might need to deprecate a11ySnapshot

bennypowers · 2026-05-25T07:57:09Z

Closing: maintainers agreed to ship EOL deprecation and node:test migration before TS upgrade. Keeping branch for reference.

This was referenced Mar 16, 2026

chore: migrate tests from mocha/chai to node:test #3044

Closed

feat!: require Node 24 and migrate CJS to ESM output #3045

Closed

feat!: migrate parse5 to v8 and convert JSDoc packages to TypeScript #3046

Draft

bennypowers marked this pull request as draft March 17, 2026 18:34

This was referenced Mar 24, 2026

feat!: migrate tests to node:test and require Node 24 #3049

Draft

refactor: use import type for type-only imports #3052

Merged

bennypowers added 23 commits March 26, 2026 14:48

fix: upgrade prettier-plugin-package to v2 for prettier 3 compat

6730d95

prettier-plugin-package v1.x requires prettier ^2, which conflicts with our upgrade to prettier ^3.7.1. v2.0.0 supports prettier ^3. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: add return type annotation to mocks preset for TS 5.9 compat

bc27cec

TS 5.9 with module:nodenext requires explicit return type annotation when the inferred type references a non-portable path (TS2742). Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: remove junk files accidentally committed

c1822b0

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: regenerate package-lock.json

0753714

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: regenerate package-lock.json after dep changes

5e8634b

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: restore parse5-utils main/exports to master (src/index.js)

2c4ac3f

The dist/index.js path was from PR4's JSDoc→TS conversion. On PR1, parse5-utils is still a JSDoc package with main: src/index.js. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: regenerate package-lock.json for parse5 v6

fd1a915

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bennypowers added 15 commits March 26, 2026 15:27

fix: remove leaked test file

3929b27

Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: add argsIgnorePattern to no-unused-vars eslint rule

a0a0ea0

Allow unused function arguments prefixed with underscore. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: rewrite remaining .js imports on multi-line from clauses

bb0f892

The previous sed only matched lines starting with import/export, missing multi-line imports where 'from' is on a continuation line. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: update prettier script paths for v3 and format files

1a754a8

prettier v3 no longer has bin-prettier.js. Use npx prettier instead. Format files that were changed but not auto-formatted. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

fix: resolve rebase conflicts from import-type PR

ebfbe33

Fix missing .ts extensions and mangled imports from rebase onto node24/import-type base branch. Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bennypowers changed the base branch from master to node24/import-type March 26, 2026 13:35

bennypowers force-pushed the node24/typescript-upgrade branch from d7b44b2 to ebfbe33 Compare March 26, 2026 13:36

chore: drop EOL Node versions, require >=22.0.0

05a5207

Node 18 and 20 are EOL. Bump engines to >=22.0.0 across all packages. CI matrix now tests 22, 24, and latest (26). Assisted-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

bennypowers force-pushed the node24/import-type branch 3 times, most recently from 33a92c0 to 5f48b6c Compare May 14, 2026 08:25

Base automatically changed from node24/import-type to master May 14, 2026 10:39

web-padawan reviewed May 23, 2026

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bennypowers closed this May 25, 2026

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chore: upgrade TypeScript to 5.9.3 and enable .ts imports#3043

chore: upgrade TypeScript to 5.9.3 and enable .ts imports#3043
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		@@ -1,4 +1,4 @@
		import { Middleware } from 'koa';
		import type { Middleware } from 'koa';

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bennypowers commented Mar 16, 2026 •

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