How can I run multiple npm scripts in parallel?

When you need to run multiple npm scripts in parallel, you can use several different methods. Here I will introduce several common approaches:

1. Using npm's & Operator

In npm scripts, you can leverage the UNIX-style & operator to execute commands concurrently. For instance, if you have two scripts script1 and script2, you can define them in the scripts section of your package.json as follows:

json
"scripts": {
  "run-parallel": "npm run script1 & npm run script2"
}

Running npm run run-parallel will initiate script1 and script2 in parallel. However, note that this method may not function as expected in Windows command-line environments, as Windows does not fully support the & operator.

2. Using npm's && Operator (Not Parallel)

Although the && operator is commonly used for sequential execution of multiple npm scripts, combining it with & can facilitate parallel execution in specific scenarios. For example:

json
"scripts": {
  "run-parallel": "npm run script1 & npm run script2 && wait"
}

Here, script1 and script2 run concurrently, and the wait command pauses execution until the background processes complete. However, this technique works in some UNIX systems but is not universally supported across all environments due to the wait command.

3. Using npm Packages like npm-run-all or concurrently

For superior cross-platform compatibility and granular control over parallel script execution, consider using npm packages such as npm-run-all or concurrently. Below is an example with npm-run-all:

First, install npm-run-all:

bash
npm install --save-dev npm-run-all

Then, configure it in your package.json's scripts section:

json
"scripts": {
  "script1": "echo 'Running script 1'",
  "script2": "echo 'Running script 2'",
  "run-parallel": "npm-run-all --parallel script1 script2"
}

Executing npm run run-parallel will run script1 and script2 concurrently.

Among these methods, using npm-run-all or concurrently is highly recommended. They offer the best cross-platform support and enable precise management of command output and error handling. For instance, if one script fails, concurrently can be configured to halt all other scripts, while npm-run-all provides similar options for script execution control.