How to build TypeScript mono-repo project

This repository explains how to create monorepos project using npm and TypeScript.

Tools

npm cli(v7 or later)
TypeScript

Directory Structure

Put each package under the packages directory.

.
├── node_modules/
├── README.md
├── package-lock.json
├── package.json
├── packages
│   ├── x-cli
│   │   ├── lib
│   │   │   ├── cli.d.ts
│   │   │   ├── cli.js
│   │   │   ├── cli.js.map
│   │   │   ├── main.d.ts
│   │   │   ├── main.js
│   │   │   └── main.js.map
│   │   ├── package.json
│   │   ├── src
│   │   │   ├── cli.ts
│   │   │   └── main.ts
│   │   └── tsconfig.json
│   └── x-core
│       ├── lib
│       │   ├── index.d.ts
│       │   ├── index.js
│       │   └── index.js.map
│       ├── package.json
│       ├── src
│       │   └── index.ts
│       └── tsconfig.json
├── tsconfig.build.json
└── tsconfig.json

Workspaces

Using npm workspaces feature, configure the following files:

Open package.json and append the workspaces key.

/* package.json */

{
  "name": "npm-ts-workspaces-example",
  "private": true,
  ...
  "workspaces": ["packages/*"]
}

Exec npm install. After successful running, all dependencies included from each package are downloaded under the repository root node_modules directory.

Dependencies across packages

In this example, the x-cli package depends on another package, x-core. So to execute (or test) x-cli, x-core packages should be installed. But in development the x-core package is not published so you can't install it.

For example, packages/x-cli/src/main.spec.ts is a test code for main.ts, which depends on packages/x-core/src/index.ts .

/* packages/x-cli/src/main.ts.*/

import { awesomeFn } from "@quramy/x-core";

export async function main() {
  // dependencies across child packages
  const out = await awesomeFn();
  return out;
}

So we need to link x-core package from x-cli to execute the x-cli 's test.

Workspaces feature of npm also solves this problem. npm i creates sim-links of each package into the top-level node_modules dir.

Resolve dependencies as TypeScript projects

As mentioned above, npm cli resolves dependencies across packages. It's enough for "runtime". However considering TypeScript sources, in other words "static", it's not.

We need to tell "x-cli package depends on x-core" to TypeScript compiler. TypeScript provides much useful feature to do this, "Project References".

First, you add composite: true to project-root tsconfig.json to use project references feature.

/* tsconfig.json */

{
  "compilerOptions": {
    ...
    "composite": true
  }
}

Second, configure each package's tsconfig and configure dependencies across packages.

/* packages/x-cli/tsconfig.json */

{
  "extends": "../../tsconfig.json",
  "compilerOptions": {
    "rootDir": "src",
    "outDir": "lib"
  },
  "references": [{ "path": "../x-core" }]
}

And create a project which depends on all packages:

/* tsconfig.build.json */

{
  "files": [],
  "references": [{ "path": "packages/x-core" }, { "path": "packages/x-cli" }]
}

Let's exec npx tsc --build tsconfig.build.json. The .ts files included in all packages are build at once!

Do we still need Lerna ?

Partially, yes.

TypeScript project references and npm workspaces features resolves dependencies across each package in both runtime and compile. So we no longer need lerna bootstrap .

But npm cli don't have functions provided by lerna's sub command, such as lerna version or lerna run. If you want them, you can use lerna or consider introducing another CLI.

Updated

Since npm CLI 7.7.0, we can use --workspaces option.

# Excecute npm test in all workspaces
$ npm test --workspaces

This option works as well as lerna run test .

License

The MIT License (MIT)

p2227/npm-ts-workspaces-example