Run Node.js scripts from the command line

The usual way to run a Node.js program is to run the globally available node command (once you install Node.js) and pass the name of the file you want to execute.

If your main Node.js application file is app.js, you can call it by typing:

node app.js

Above, you are explicitly telling the shell to run your script with node. You can also embed this information into your JavaScript file with a "shebang" line. The "shebang" is the first line in the file, and tells the OS which interpreter to use for running the script. Below is the first line of JavaScript:

#!/usr/bin/node

Above, we are explicitly giving the absolute path of interpreter. Not all operating systems have node in the bin folder, but all should have env. You can tell the OS to run env with node as parameter:

#!/usr/bin/env node

// your javascript code

To use a shebang, your file should have executable permission. You can give app.js the executable permission by running:

chmod u+x app.js

While running the command, make sure you are in the same directory which contains the app.js file.

Pass string as argument to node instead of file path

To execute a string as argument you can use -e, --eval "script". Evaluate the following argument as JavaScript. The modules which are predefined in the REPL can also be used in script.

On Windows, using cmd.exe a single quote will not work correctly because it only recognizes double " for quoting. In Powershell or Git bash, both ' and " are usable.

node -e "console.log(123)"

Restart the application automatically

As of Node.js V16, there is a built-in option to automatically restart the application when a file changes. This is useful for development purposes. To use this feature, you need to pass the --watch flag to Node.js.

node --watch app.js

So when you change the file, the application will restart automatically. Read the --watch flag documentation.

Run a task with Node.js

Node.js provides a built-in task runner that allows you to execute specific commands defined in your package.json file. This can be particularly useful for automating repetitive tasks such as running tests, building your project, or linting your code.

Using the --run flag

The --run flag allows you to run a specified command from the scripts section of your package.json file. For example, if you have the following package.json:

{
  "type": "module",
  "scripts": {
    "start": "node app.js",
    "dev": "node --run -- --watch",
    "test": "node --test"
  }
}

You can run the test script using the --run flag:

node --run test

Passing arguments to the command

Let's explain the dev key in the scripts object of the package.json file.

The syntax -- --another-argument is used to pass arguments to the command. In this case, the --watch argument is passed to the dev script.

node --run dev

Environment variables

The --run flag sets specific environment variables that can be useful for your scripts:

• NODE_RUN_SCRIPT_NAME: The name of the script being run.
• NODE_RUN_PACKAGE_JSON_PATH: The path to the package.json file being processed.

Intentional limitations

The Node.js task runner is intentionally more limited compared to other task runners like npm run or yarn run. It focuses on performance and simplicity, omitting features like running pre or post scripts. This makes it suitable for straightforward tasks but may not cover all use cases.