Node.js Live Restarts with Nodemon and Watch

Learn how to use nodemon and watch to automatically restart your Node.js server whenever you make changes. A must-read for Node.js developers.

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:

• send a signal so you can gracefully handle a shutdown
• trigger events when nodemon’s state changes
• pipe output to other processes
• load nodemon as a module into your project
• spawn nodemon as a child process, and
• use nodemon in Gulp and Grunt workflows.

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

#node #nodejs