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How to build TypeScript mono-repo project with yarn and lerna
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README.md

How to build TypeScript mono-repo project

CircleCI

Tools

  • yarn: NPM client.
  • Lerna: Multiple packages management tool.
  • TypeScript: ^3.0.0 supports project references.

If you use ts(<= 2.9), see ts-2.x branch.

Directory Structure

Put each package under the packages directory.

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

Workspaces

Using yarn workspace feature, configure the following files:

  • /package.json

Append the workspaces key.

{
  "private": true,
  "workspaces": [
    "packages/*"
  ]
}
  • lerna.json

Set npmClient "yarn" and turn useWorkspaces on.

{
  "lerna": "2.2.0",
  "packages": [
    "packages/*"
  ],
  "npmClient": "yarn",
  "useWorkspaces": true,
  "version": "1.0.0"
}

Exec yarn install(or lerna bootstrap). After successful running, all dependency packages are downloaded under the repository root node_modules directory.

Dependencies between 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.

yarn solves this problem. This command creates sim-links of each package into the top-level node_modules dir.

Resolve Dependencies as TypeScript Modules

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

For example, the following code depends a module x-core located at other package.

/* packages/x-cli/src/main.ts */
import { awesomeFn } from "@quramy/x-core";

export function cli() {
  awesomeFn();
  return Promise.resolve(true);
}

If you compile this code, TypeScript compiler emits a "Cannot find module" error until building x-core package and creating x-core/index.d.ts. And it's silly to compile dependent packages(e.g. x-core) in the same repository after each editing them.

TypeScript's path mapping is the best solution. Path mappings are declared such as:

/* tsconfig.json */
{
  "compilerOptions": {
    /* other options */
    "baseUrl": "./packages",
    "paths": {
      "@quramy/*": ["./*/src"]
    }
  }
}

The above setting means import { awesomeFn } from "@quramy/x-core" is mapped to import { awesomeFn } from "../../x-core/src"(it's relative from "packages/x-cli/src/main.ts"). In other words, path mapping allows to treat developing packages' sources as published(compiled) modules.

References between packages

TypeScript 3.0 supports Project reference feature. You can tell tsc that x-cli depends on x-core project using this.

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

In the above json, the key references means the dependency.

Compile all packages

Our repository has multiple tsconfig.json files. We can compile all packages with "-b" option:

$ tsc -b packages/x-core packages/x-cli

License

The MIT License (MIT)

Copyright 2017 Quramy

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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