For use during development of a node.js based application.
nodemon will watch the files in the directory that nodemon was started, and if they change, it will automatically restart your node application.
nodemon does not require any changes to your code or method of development. nodemon simply wraps your node application and keeps an eye on any files that have changed. Remember that nodemon is a replacement wrapper for node, think of it as replacing the word "node" on the command line when you run your script.
Either through forking or by using npm (the recommended way):
npm install nodemon -g
And nodemon will be installed in to your bin path. Note that as of npm v1, you must explicitly tell npm to install globally as nodemon is a command line utility.
nodemon wraps your application, so you can pass all the arguments you would normally pass to your app:
nodemon [your node app]
For example, if my application accepted a host and port as the arguments, I would start it as so:
nodemon ./server.js localhost 8080
Any output from this script is prefixed with [nodemon], otherwise all output from your application, errors included, will be echoed out as expected.
nodemon also supports running and monitoring coffee-script apps:
nodemon server.coffee
If no script is given, nodemon will test for a package.json file and if found, will run the file associated with the main property (ref).
You can also pass the debug flag to node through the command line as you would normally:
nodemon --debug ./server.js 80
If you have a package.json file for your app, you can omit the main script entirely and nodemon will read the package.json for the main property and use that value as the app.
nodemon was original written to restart hanging processes such as web servers, but now supports apps that cleanly exit. If your script exits cleanly, nodemon will continue to monitor the directory (or directories) and restart the script if there are any changes.
nodemon can also be used to execute and monitor other programs. nodemon will read the file extension of the script being run and monitor that extension instead of .js if there's no .nodemonignore:
nodemon --exec "python -v" ./app.py
Now nodemon will run app.py with python in verbose mode (note that if you're not passing args to the exec program, you don't need the quotes), and look for new or modified files with the .py extension.
By default nodemon monitors the current working directory. If you want to take control of that option, use the --watch option to add specific paths:
nodemon --watch app --watch libs app/server.js
Now nodemon will only restart if there are changes in the ./app or ./libs directory. By default nodemon will traverse sub-directories, so there's no need in explicitly including sub-directories.
In some situations, you may want to wait until a number of files have changed. The timeout before checking for new file changes is 1 second. If you're uploading a number of files and it's taking some number of seconds, this could cause your app to restart multiple time unnecessarily.
To add an extra throttle, or delay restarting, use the --delay command:
nodemon --delay 10 server.js
The delay figure is number of seconds to delay before restarting. So nodemon will only restart your app the given number of seconds after the last file change.
By default, if nodemon will only restart when a .js JavaScript file changes. In some cases you will want to ignore some specific files, directories or file patterns, to prevent nodemon from prematurely restarting your application.
You can use the example ignore file (note that this example file is not hidden - you must rename it to .nodemonignore) as a basis for your nodemon, but it's very simple to create your own:
# this is my ignore file with a nice comment at the top
/vendor/* # ignore all external submodules
/public/* # static files
./README.md # a specific file
*.css # ignore any CSS files too
The ignore file accepts:
- Comments starting with a
#symbol - Blank lines
- Specific files
- File patterns (this is converted to a regex, so you have full control of the pattern)
nodemon sends a kill signal to your application when it sees a file update. If you need to clean up on shutdown inside your script you can capture the kill signal and handle it yourself.
The following example will listen once for the SIGUSR2 signal (used by nodemon to restart), run the clean up process and then kill itself for nodemon to continue control:
process.once('SIGUSR2', function () {
gracefulShutdown(function () {
process.kill(process.pid, 'SIGUSR2');
})
});
Note that the process.kill is only called once your shutdown jobs are complete. Hat tip to Benjie Gillam for writing technique this up.
If you're using nodemon with forever (perhaps in a production environment) you can combine the two together. This way if the script crashes, forever restarts the script, and if there are file changes, nodemon restarts your script. For more detail, see issue 30.
To acheive this you need to include the --exitcrash flag to ensure nodemon exits if the script crashes (or exits unexpectedly):
forever nodemon --exitcrash server.js
To test this, you can kill the server.js process and forever will restart it. If you touch server.js nodemon will restart it.
Note that I would not recommend using nodemon in a production environment - but that's because I wouldn't want it restart without my explicit instruction.
nodemon has three potential methods it uses to look for file changes. First, it polls using the find command to search for files modified within the last second. This method works on systems with a BSD based find (Mac, for example).
Next it tries using node's fs.watch. fs.watch will not always work however, and nodemon will try and detect if this is the case by writing a file to the tmp directory and seeing if fs.watch is triggered when it's removed. If nodemon finds that fs.watch was not triggered, it will then fall back to the third method (called legacy watch), which works by statting each file in your working directory looking for changes to the last modified time. This is the most cpu intensive method, but it may be the only option on some systems.
In certain cases, like when where you are working on a different drive than your tmp directory is on, fs.watch may give you a false positive. You can force nodemon to start using the most compatible legacy method by passing the -L switch, e.g. nodemon -L /my/odd/file.js.