JavaScript

Using Nodemon and Watch in Node.js for Live Restarts

Craig Buckler
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Node.js development can be slower than necessary if you have to stop and restart your new application every time you make a change. This tutorial provides two solutions to improve your coding workflow.

Table of Contents

If you’ve ever developed a PHP application, you’ll know you can make updates and refresh your browser to test the changes. A web server such as Apache or NGINX receives a your request for a PHP file, then passes the content to a PHP interpreter which executes the code. The server returns resulting output (typically HTML or JSON) to the calling browser. In other words, the code runs dynamically on every request.

Node.js takes a different approach for web apps: your JavaScript application is a web server. Running node index.js initializes the app, loads all modules, and launches a server which can respond to incoming requests. Changing a file makes no difference to the app’s output because it’s already running in memory. To test updates, you must shut it down with Ctrl | Cmd + C and run node index.js again.

Node’s stop and restart process becomes frustrating when you’re making lots of changes during debugging or those rare times of undisturbed productivity. Fortunately, there are two solutions:

  1. nodemon
  2. Node.js –watch mode

nodemon

nodemon is a third-party Node.js module developed by JavaScript guru Remy Sharp. (He says you can pronounce it as you choose!)

You can install nodemon as a global module:

npm install -g nodemon

Then replace node with nodemon in development start-up commands. For example, consider this command:

node --inspect index.js arg1 arg2

The command above will now look like this:

nodemon --inspect index.js arg1 arg2

Your application starts as normal, but it will automatically restart when you edit and save a source file. There’s no need to press Ctrl | Cmd + C and run again, although you can type rs and press Enter to force a restart.

Note: nodemon is a server-side solution and doesn’t refresh any browser tabs you have pointed at your app. You can implement live reloading with tools such as Browsersync or esbuild.

For nodemon help, enter:

nodemon --help

nodemon Configuration

nodemon has its own set of command-line arguments which take priority over configuration elsewhere. You can also define configuration in:

  • a "nodemonConfig" section in your project’s package.json file
  • a local nodemon.json configuration file in the project directory, and/or
  • a global nodemon.json configuration file used when running nodemon --config <file> from the command line

The following parameters/settings can are commonly used.

watch

nodemon monitors JavaScript files in the current working directory, but you can explicitly set specific paths with wildcards on the command line:

nodemon --watch lib1 config/*.json ./index.js

Or you can do this in a nodemon.json configuration file:

{
  "watch": [
    "lib1",
    "config/*.json"
  ]
}

ignore

Similarly, you can choose to ignore paths:

nodemon --ignore lib2 config/build.json ./index.js

Or you can do this in a nodemon.json configuration file:

{
  "ignore": [
    "lib2",
    "config/build.json"
  ]
}

ext

You can monitor specific files by their extension. For example, you can monitor js, cjs, mjs, json, and njk template files like so:

nodemon --ext "js,cjs,mjs,json,njk" ./index.js

Or you can do so in a nodemon.json configuration file:

{
  "ext": "js,cjs,mjs,json,njk"
}

legacyWatch

File watching can fail in some environments, such as Docker containers reading files from a mounted drive. Switching to legacy watch mode uses polling to check whether files have changed. From the command line:

nodemon --legacy-watch ./index.js

Or in a nodemon.json configuration file:

{
  "legacyWatch": true
}

delay

nodemon waits one second before triggering a restart. This can be useful when you’re typically saving many files at once. You can change the delay from the command line — for example, to five seconds:

nodemon --delay 5 ./index.js

Or in a nodemon.json configuration file (note this uses milliseconds rather than seconds):

{
  "delay": 5000
}

verbose

Shows verbose output logs:

nodemon --verbose ./index.js

Or in a nodemon.json configuration file:

{
  "verbose": true
}

env

Sets specific environment variables a nodemon.json configuration file:

{
  "env": {
    "NODE_ENV": "development",
    "SERVER_PORT": 8000
  }
}

Other executables

Finally, you can launch applications written in other languages using nodemon. For example, to start a perl script which restarts automatically:

nodemon --exec "perl" ./app.pl

You can also define lists of executables in a nodemon.json configuration file with their extension name:

{
  "execMap": {
    "pl": "perl"
  }
}

Advanced nodemon

nodemon provides more advanced functionalit,y should you require it:

Node.js --watch Mode

nodemon remains the tool of choice if you have sophisticated application start-up requirements. However, if you’re using Node.js 18.11 (released late 2022) or newer, it provides an experimental --watch option to restart your app without having to install a nodemon or any other third party module. For example, to the start command:

node --inspect index.js

This becomes:

node --inspect --watch index.js

Node.js restarts when any imported file changes. There are no other control options, so if it’s not suitable for your project, consider using nodemon instead.

Summary

Auto restarting your Node.js app is something you’ll find increasingly useful as your experience increases. Consider it as part of your development workflow in all your projects.