Mastering npm-run-script: Comprehensive Guide and API Examples

The npm run-script command is a powerful tool in the npm ecosystem, allowing you to execute scripts defined in your package.json file. These scripts can help automate tasks, run tests, and manage your Node.js application. In this comprehensive guide, we will explore various aspects and APIs of npm-run-script, complete with multiple code snippets and an example application.

What is npm-run-script?

The npm run-script command lets you run any script that is defined in your package.json file under the “scripts” section. Typical use cases include running build processes, starting servers, or executing test suites.

Defining Scripts in package.json

Scripts are defined in the package.json file under the “scripts” field. You can name these scripts anything you like, and invoke them using npm run <script-name>.

  {
  "name": "example-app",
  "version": "1.0.0",
  "scripts": {
    "start": "node app.js",
    "build": "babel src -d lib",
    "test": "jest"
  }
}  

Running Scripts

Use npm run <script-name> to execute a script:

  npm run start npm run build npm run test  

Pre and Post Scripts

npm allows you to define pre and post scripts that execute before and after a given script. Simply prefix the script name with “pre” or “post”:

  {
  "scripts": {
    "prestart": "echo 'Preparing to start!'",
    "start": "node app.js",
    "poststart": "echo 'App has started.'"
  }
}  

Running Binaries

npm-run-script allows you to run binaries declared as dependencies in your project:

  {
  "scripts": {
    "lint": "eslint .",
    "test": "jest"
  }
}  

Note: No need to specify the full path to the binary, npm will look for it in node_modules/.bin.

Using Arguments

You can pass arguments to npm scripts by separating them with --:

  {
  "scripts": {
    "build:dev": "webpack --mode development",
    "build:prod": "webpack --mode production"
  }
}  

Example Application

Below is an example structure of a Node.js application with various scripts defined:

  {
  "name": "my-node-app",
  "version": "1.0.0",
  "scripts": {
    "start": "node server.js",
    "build": "webpack --config webpack.config.js",
    "test": "jest",
    "lint": "eslint ."
  },
  "devDependencies": {
    "webpack": "^5.36.2",
    "jest": "^26.6.3",
    "eslint": "^7.23.0"
  }
}  

To start the application, run:

  npm run start  

To run tests:

  npm run test  

To lint the code:

  npm run lint  

To build the project:

  npm run build  

Understanding and mastering npm run-script is crucial for any JavaScript or Node.js developer. With the knowledge and examples provided in this guide, you should be well-equipped to automate and manage tasks in your projects effectively.

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