chore: formalize & guard ESM-only (no CJS, ESM-native) — closes #20

.changeset/esm-only-guard.md

@@ -0,0 +1,19 @@
+---
+'@svelte-vitals/core': minor
+'@svelte-vitals/vite': minor
+'svelte-vitals': patch
+'@svelte-vitals/mcp': patch
+---
+
+Formalize the ESM-only stance (#20): drop the legacy top-level `main`/`types` from
+`@svelte-vitals/core` and `@svelte-vitals/vite` so every package is `exports`-only,
+add `sideEffects: false` across all packages for consistent tree-shaking, declare
+`"engines": { "node": ">=18" }` on every package so the documented runtime floor is
+machine-enforceable, and document the ESM-only (Node 18+, `require()` unsupported by
+design) requirement in each README. CI now guards type-resolution with
+`@arethetypeswrong/cli` (esm-only profile) alongside publint.
+
+`core` and `vite` get a `minor` bump because dropping top-level `main`/`types` can
+affect consumers/tools that resolve entry points without `exports` support (e.g.
+`moduleResolution: node`); `svelte-vitals` and `@svelte-vitals/mcp` only gain the
+additive `sideEffects: false` and `engines` declaration, so they stay `patch`.

package.json

@@ -9,11 +9,14 @@
     "test": "pnpm -r test",
     "lint": "prettier --check . && eslint .",
     "format": "prettier --write .",
-    "check:publish": "pnpm --filter @svelte-vitals/core --filter @svelte-vitals/vite --filter svelte-vitals --filter @svelte-vitals/mcp exec publint",
+    "check:publish": "pnpm run check:publint && pnpm run check:types",
+    "check:publint": "pnpm --filter @svelte-vitals/core --filter @svelte-vitals/vite --filter svelte-vitals --filter @svelte-vitals/mcp exec publint",
+    "check:types": "pnpm --workspace-concurrency=1 --filter @svelte-vitals/core --filter @svelte-vitals/vite --filter svelte-vitals --filter @svelte-vitals/mcp exec attw --pack . --profile esm-only",
     "release": "changeset publish",
     "changeset": "changeset"
   },
   "devDependencies": {
+    "@arethetypeswrong/cli": "catalog:",
     "@changesets/cli": "catalog:",
     "@eslint/compat": "catalog:",
     "@eslint/js": "catalog:",

packages/cli/README.md

@@ -5,6 +5,8 @@
 
 > **A SvelteKit SEO checker — not a runtime Web Vitals reporter.**
 > Diagnose your project's SEO health by statically analyzing your source code, before it ships. No browser, no build server, no headless Chrome.
+>
+> **ESM-only** (Node 18+). Ships ES modules only; `require()` is unsupported by design.
 
 ```bash
 npx svelte-vitals

packages/cli/package.json

@@ -22,6 +22,10 @@
     "url": "https://github.com/oekazuma/svelte-vitals/issues"
   },
   "homepage": "https://github.com/oekazuma/svelte-vitals#readme",
+  "engines": {
+    "node": ">=18"
+  },
+  "sideEffects": false,
   "bin": {
     "svelte-vitals": "./dist/bin.js"
   },

packages/cli/tsup.config.ts

@@ -1,5 +1,6 @@
 import { defineConfig } from 'tsup';
 
+// ESM-only by design (issue #20) — never add 'cjs'.
 export default defineConfig({
   entry: ['src/index.ts', 'src/bin.ts'],
   format: ['esm'],

packages/core/README.md

@@ -9,6 +9,8 @@ This package is **mode-independent** and contains no I/O — it operates on a no
 
 > Most users don't depend on this directly — install [`svelte-vitals`](https://www.npmjs.com/package/svelte-vitals) instead. This package is for building tools on top of the shared engine.
 
+> **ESM-only** (Node 18+). Ships ES modules only; `require()` is unsupported by design.
+
 ## License
 
 [MIT](https://github.com/oekazuma/svelte-vitals/blob/main/LICENSE.md) © [Kazuma Oe](https://github.com/oekazuma)

packages/core/package.json

@@ -20,15 +20,16 @@
     "url": "https://github.com/oekazuma/svelte-vitals/issues"
   },
   "homepage": "https://github.com/oekazuma/svelte-vitals#readme",
+  "engines": {
+    "node": ">=18"
+  },
   "sideEffects": false,
   "exports": {
     ".": {
       "types": "./dist/index.d.ts",
       "import": "./dist/index.js"
     }
   },
-  "main": "./dist/index.js",
-  "types": "./dist/index.d.ts",
   "files": [
     "dist"
   ],

packages/core/tsup.config.ts

@@ -1,5 +1,6 @@
 import { defineConfig } from 'tsup';
 
+// ESM-only by design (issue #20) — never add 'cjs'.
 export default defineConfig({
   entry: ['src/index.ts'],
   format: ['esm'],

packages/mcp/README.md

@@ -22,4 +22,4 @@ Add to your MCP client config:
 }
 ```
 
-ESM-only. Requires Node 18+.
+**ESM-only** (Node 18+). Ships ES modules only; `require()` is unsupported by design.

packages/mcp/package.json

@@ -22,6 +22,10 @@
     "url": "https://github.com/oekazuma/svelte-vitals/issues"
   },
   "homepage": "https://github.com/oekazuma/svelte-vitals#readme",
+  "engines": {
+    "node": ">=18"
+  },
+  "sideEffects": false,
   "bin": {
     "svelte-vitals-mcp": "./dist/bin.js"
   },

packages/vite/README.md

@@ -4,6 +4,8 @@
 
 Vite/SvelteKit plugin for [svelte-vitals](https://github.com/oekazuma/svelte-vitals). It piggybacks on `vite build`, parses the **prerendered HTML's `<head>`**, and runs the same SEO rules as the CLI — library-agnostic, because it inspects the real output. Fails the build when findings reach `failOn`.
 
+> **ESM-only** (Node 18+). Ships ES modules only; `require()` is unsupported by design.
+
 ## Usage
 
 ```ts

packages/vite/package.json

@@ -21,6 +21,10 @@
     "url": "https://github.com/oekazuma/svelte-vitals/issues"
   },
   "homepage": "https://github.com/oekazuma/svelte-vitals#readme",
+  "engines": {
+    "node": ">=18"
+  },
+  "sideEffects": false,
   "exports": {
     ".": {
       "types": "./dist/index.d.ts",
@@ -31,8 +35,6 @@
       "import": "./dist/hooks/index.js"
     }
   },
-  "main": "./dist/index.js",
-  "types": "./dist/index.d.ts",
   "files": [
     "dist"
   ],

packages/vite/tsup.config.ts

@@ -1,5 +1,6 @@
 import { defineConfig } from 'tsup';
 
+// ESM-only by design (issue #20) — never add 'cjs'.
 export default defineConfig({
   entry: ['src/index.ts', 'src/hooks/index.ts'],
   format: ['esm'],