How to run watch script in pnpm workspace

Running watch scripts in a pnpm workspace typically involves monitoring changes to files across multiple packages and executing specific tasks, such as recompiling code or running tests. pnpm is a package manager particularly well-suited for monorepo project structures, which contain multiple interdependent packages.

To set up watch scripts in a pnpm workspace, follow these steps:

1. Setting up watch scripts within individual packages: First, ensure each package's package.json includes a watch script. For example, if you're using TypeScript, you might want to automatically compile your source code when changes occur. You can use the watch mode of the tsc command:

   json
   {
     "scripts": {
       "watch": "tsc --watch"
     }
   }

2. Using pnpm's -r or --recursive flag: To run watch scripts across the entire workspace, use pnpm's -r or --recursive flag to execute commands recursively. For example:

   sh
   pnpm watch -r

3. Leveraging the pnpm-workspace.yaml configuration file: pnpm allows you to define workspace packages in the pnpm-workspace.yaml file. Place this file in the workspace root and configure it correctly so pnpm recognizes which packages belong to the workspace.

4. Running scripts in parallel or sequentially: You might want to run watch scripts in parallel or sequentially. pnpm handles scripts as follows:

   • Parallel (default): To run all watch scripts simultaneously, omit the --parallel flag, as this is the default behavior of pnpm -r.
   • Sequential: To run watch scripts one after another, use the --serial flag:

     sh
     pnpm watch -r --serial

5. Handling output: When running multiple watch scripts, log output can become extensive. pnpm provides the --filter flag to limit which packages execute the command, helping you manage output more effectively. For example, to run the watch script for a specific package:

   sh
   pnpm watch --filter=specific-package-name

6. Using third-party tools: For advanced watch functionality, such as triggering recompilation only when dependencies change, consider third-party tools like lerna or nx, which offer more sophisticated workspace management capabilities.

7. Example: Suppose you have a workspace with two packages: package-a and package-b, where package-a depends on package-b. If you modify package-b, you might want package-a to automatically recompile. Set up a watch script in package-a's package.json that monitors changes to package-b and triggers recompilation:

   package-a/package.json:

   json
   {
     "scripts": {
       "watch": "watch 'pnpm build' ../package-b/src"
     }
   }

   Here, watch is a hypothetical command. In practice, you'll need a tool that can monitor file changes, such as chokidar-cli.

By following these steps and considering these factors, you can effectively run watch scripts in a pnpm workspace.