npm-run-parallel

Run npm tasks in parallel and exit when they are all done.

Installation

Locally (recommended, especially with npm scripts):

npm install npm-run-parallel

Globally, as a CLI:

npm install -g npm-run-parallel

Usage

From the command line, or an npm script:

npm-run-parallel <npm scripts>

So, if I want to run npm install and npm test in parallel (a contrived example, I know!):

npm-run-parallel install test

The process will complete when both npm install and npm test finish.

Note: you can run custom npm scripts, too. Just like you would install or test above.

Why?

On a given project, there are likely some long or expensive npm scripts, like asset compilation or multi-directory dependency installs. It's faster to do these in parallel.

A common way to run any shell command (which an npm script is) is the & operator, which creates a subprocess. This subprocess runs separately, so the original process can never tell how or when the subprocess ended. In a similar vein, the | operator can pipe the output of one command to another. This can feel like streaming, but passing the output of one npm script to another is both a hack and prone to erroring out.

Some build tools, like gulp, accomplish parallel commands (a.k.a. tasks) with streaming libraries. The recent trend towards npm scripts from these walled-garden tools necessitated emulating that functionality. So npm-run-parallel all the tasks!

Local development

• npm run watch - Compile source code, and watch for changes

• npm run lint - Lints source code (eslint)

• npm run test:watch - Run tests and watch for file changes

Other commands

• npm run build - Compiles source code (also used in prepublish)

• npm run test - Run unit tests once

• npm run start -- - Emulates the cli interface (note: pass it task arguments. Useful for manual testing.)