Build with the effeck CLI

effeck replaces tsc. It checks .effeck and .ts files as one program, emits JavaScript, and accepts TypeScript's compiler flags. Install the packages with Add Effeck to an existing project first.

1. Configure tsconfig.json

If the project has no tsconfig.json, create this one. It selects .effeck files under src/ and emits Node ESM to dist/:

{
  "compilerOptions": {
    "target": "ES2022",
    "module": "NodeNext",
    "moduleResolution": "NodeNext",
    "strict": true,
    "sourceMap": true,
    "rootDir": "src",
    "outDir": "dist",
    "noEmitOnError": true,
    "rewriteRelativeImportExtensions": true,
    "skipLibCheck": true,
    "types": []
  },
  "include": ["src/**/*.effeck"]
}

If the project has a tsconfig.json, keep it, and check that include selects .effeck files. A directory entry such as "src" selects them. A glob such as "src/**/*.ts" does not; add "src/**/*.effeck" beside it.

2. Replace tsc in the scripts

In package.json, replace tsc with effeck in every script. If the project has no build script, add these:

{
  "scripts": {
    "build": "effeck",
    "start": "effeck && node --enable-source-maps dist/main.js",
    "test": "vitest run"
  }
}

effeck with no arguments checks and emits the project, effeck --noEmit only checks it, effeck --watch rebuilds on every save, and effeck -b builds project references.

3. Compile a first module

Create src/hello.effeck, in a directory that include selects:

// src/hello.effeck
export function hello(name: string) {
  return `Hello, ${name}!`
}

Run npx effeck. It prints nothing, exits with status 0, and writes hello.js to the outDir, dist/ in the configuration above.

In .effeck files, import local modules by their source name: import { hello } from "./hello.effeck". In .ts files, import ./hello.js, which resolves to hello.effeck.

4. Test with Vitest

Create vitest.config.ts, which compiles .effeck tests through effeck-vite:

// TypeScript (.ts)
// vitest.config.ts
import { defineConfig } from "vitest/config"
import effeck from "effeck-vite"

export default defineConfig({
  plugins: [effeck()],
  test: { include: ["src/**/*.test.effeck"] }
})

Create src/hello.test.effeck:

// src/hello.test.effeck
import { assert, it } from "@effect/vitest"
import { hello } from "./hello.effeck"

it.effect("says hello") {
  assert.strictEqual(hello("Effeck"), "Hello, Effeck!")
}

Run npx vitest run. The output includes:

 Test Files  1 passed (1)
      Tests  1 passed (1)

Tell the user that you added src/hello.effeck and src/hello.test.effeck. They can keep them as a starting point or delete them.

Next

Set up the editor: VS Code and Cursor, Neovim, Zed, or other editors. Then verify the setup with step 4 of Set up Effeck.