Tutorial

How To Restart Your Node.js Apps Automatically with nodemon

Node.js

Introduction

In Node.js, you need to restart the process to make changes take effect. This adds an extra step to your workflow to have the changes take place. You can eliminate this extra step by using nodemon to restart the process automatically.

nodemon is a command-line interface (CLI) utility developed by @rem that wraps your Node app, watches the file system, and automatically restarts the process.

In this article, you will learn about installing, setting up, and configuring nodemon.

Prerequisites

If you would like to follow along with this article, you will need:

Step 1 — Installing nodemon

First, you will need to install nodemon on your machine. Install the utility either globally or locally on your project using npm or Yarn:

Global Installation

You can install nodemon globally with npm:

  • npm install nodemon -g

Or with Yarn:

  • yarn global add nodemon

Local Installation

You can also install nodemon locally with npm. When performing a local installation, we can install nodemon as a dev dependency with --save-dev (or --dev):

  • npm install nodemon --save-dev

Or with Yarn:

  • yarn add nodemon --dev

One thing to be aware of with a local install is you won’t be able to use the nodemon command directly from the command line:

Output
  • command not found: nodemon

However, you can use it as part of some npm scripts or with npx.

This concludes the nodemon installation process. Next, we will use nodemon with our projects.

Step 2 — Setting Up an Example Express Project with nodemon

We can use nodemon to start a Node script. For example, if we have an Express server setup in a server.js file, we can start it and watch for changes like this:

  • nodemon server.js

You can pass in arguments the same way as if you were running the script with Node:

  • nodemon server.js 3006

Every time you make a change to a file with one of the default watched extensions (.js, .mjs, .json, .coffee, or .litcoffee) in the current directory or a subdirectory, the process will restart.

Let’s assume we write an example server.js file that outputs the message: Dolphin app listening on port ${port}!.

We can run the example with nodemon:

  • nodemon server.js

We see the following terminal output:

Output
[nodemon] 1.17.3 [nodemon] to restart at any time, enter `rs` [nodemon] watching: *.* [nodemon] starting `node server.js` Dolphin app listening on port 3000!

While nodemon is still running, let’s make a change to the server.js file to output the message: Shark app listening on port ${port}!.

We see the following additional terminal output:

Output
[nodemon] restarting due to changes... [nodemon] starting `node server.js` Shark app listening on port 3000!

The terminal output from our Node.js app is displaying as expected. You can restart the process at any time by typing rs and hitting ENTER.

Alternatively, nodemon will also look for a main file specified in your project’s package.json file:

package.json
{
  // ...
  "main": "server.js",
  // ...
}

Or, a start script:

package.json
{
  // ...
  "scripts": {
    "start": "node server.js"
  },
  // ...
}

Once you make the changes to package.json, you can then call nodemon to start the example app in watch mode without having to pass in server.js.

Step 3 — Using Options

You can modify the configuration settings available to nodemon.

Let’s go over a few of the main options:

  • --exec: Use the --exec switch to specify a binary to execute the file with. For example, when combined with the ts-node binary, --exec can become useful to watch for changes and run TypeScript files.
  • --ext: Specify different file extensions to watch. For this switch, provide a comma-separated list of file extensions (e.g., --ext js,ts).
  • --delay: By default, nodemon waits for one second to restart the process when a file changes, but with the --delay switch, you can specify a different delay. For example, nodemon --delay 3.2 for a 3.2-second delay.
  • --watch: Use the --watch switch to specify multiple directories or files to watch. Add one --watch switch for each directory you want to watch. By default, the current directory and its subdirectories are watched, so with --watch you can narrow that to only specific subdirectories or files.
  • --ignore: Use the --ignore switch to ignore certain files, file patterns, or directories.
  • --verbose: A more verbose output with information about what file(s) changed to trigger a restart.

You can view all the available options with the following command:

  • nodemon --help

Using these options, let’s create the command to satisfy the following scenario:

  • watching the server directory
  • specifying files with a .ts extension
  • ignoring files with a .test.ts suffix
  • executing the file (server/server.ts) with ts-node
  • waiting for three seconds to restart after a file changes
  • nodemon --watch server --ext ts --exec ts-node --ignore '*.test.ts' --delay 3 server/server.ts

This command combines --watch, --ext, --exec, --ignore, and --delay options to satisfy the conditions for our scenario.

Step 4 — Using Configurations

In the previous example, adding configuration switches when running nodemon can get quite tedious. A better solution for projects that need specific configurations is to specify these configs in a nodemon.json file.

For example, here are the same configurations as the previous command line example, but placed in a nodemon.json file:

nodemon.json
{
  "watch": ["server"],
  "ext": "ts",
  "ignore": ["*.test.ts"],
  "delay": "3",
  "execMap": {
    "ts": "ts-node"
  }
}

Note the use of execMap instead of the --exec switch. execMap allows you to specify binaries that should be used given certain file extensions.

Alternatively, if you’d rather not add a nodemon.json config file to your project, you can add these configurations to the package.json file under a nodemonConfig key:

package.json
{
  "name": "test-nodemon",
  "version": "1.0.0",
  "description": "",
  "nodemonConfig": {
    "watch": [
      "server"
    ],
    "ext": "ts",
    "ignore": [
      "*.test.ts"
    ],
    "delay": "3",
    "execMap": {
      "ts": "ts-node"
    }
  },
  // ...

Once you make the changes to either nodemon.json or package.json, you can then start nodemon with the desired script:

  • nodemon server/server.ts

nodemon will pick up the configurations and use them. This way, your configurations can be saved, shared, and repeated to avoid copy-and-pasting or typing errors in the command line.

Conclusion

In this article, you explored how to use nodemon with your Node.js applications. This tool helps automate the process of stopping and starting a Node server to view the changes.

For more information about the available features and troubleshooting errors, consult the official documentation.

If you’d like to learn more about Node.js, check out our Node.js topic page for exercises and programming projects.

0 Comments

Creative Commons License