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!