Nodemon for Deno
UppubDate: As of Deno v1.4, there is a built in watch mode that you can enable with the --watch flag. Read more about that here.
Nodemon, or as I read it in my head Nodémon!, is a utility for restarting Node.js processes when the source changes. It’s is the first dev dependency I add when working in Node, because it is so handy!
Deno, the secure runtime for JavaScript and TypeScript, doesn’t work with Nodemon. When I first started building with Deno, I was reminded just how annoying it is to stop and start your server whenever there is a change.
Enter denon, the “replacement” for Nodemon in Deno land. As long as you’re using deno@^1.0.1, you can get all the goodness of automattic restarting with denon.
Install
You can install denon with Deno’s install command:
deno install --allow-read --allow-run --allow-write --allow-net -f --unstable https://deno.land/x/denon@v2.2.0/denon.ts
That command installs denon version 2.2.0, so reference the documentation for the most up-to-date instructions.
Simple usage
Once you have denon installed, you can use it as a straight replacement for all deno commands:
# With Deno
deno run --allow-net https://deno.land/std/examples/echo_server.ts
# With denon
denon run --allow-net https://deno.land/std/examples/echo_server.ts
This is the same behavior as node/nodemon. But running external code doesn’t really illustrate the value of denon.
To see it in action, copy echo_server.ts locally and then run with denon:
denon run --allow-net echo_server.ts
Now when you make any changes to the source, you will see denon automatically restart the server.
Configuration
My favorite feature of denon is its configuration file: denon.json. With it, you get some of the “scripts” features of Node.js’s package.json that are currently missing in Deno.
To create a configuration file, you can call denon with the --init flag:
denon --init
This will create a denon.json file where you can include scripts with commands, permissions, and environment variables.
We can create a “start” script for the echo_server.ts like so:
{
"$schema": "https://deno.land/x/denon/schema.json",
"scripts": {
"start": {
"cmd": "deno run echo_server.ts",
"desc": "Start echo_server in watch mode",
"allow": ["env", "net"],
"env": {
"PORT": "2525"
}
}
}
}
Our “start” script has a command, description, permissions to allow, and an environment variable PORT that we are passing to our server.
To run the script, type:
denon start
And you’re off to the races! I love the ability to start a Deno process without typing all those permissions. :chefs-kiss:
Learn more
The denon documentation lists the full feature set and includes a bunch of helpful examples. Make sure to check that out when setting up denon on your next Deno project.
Happy coding!