About

Deno can run JavaScript and TypeScript with no additional tools or configuration required, unlike Node which will require some additional libraries and configurations to work with it.

Additionally Deno by default can work as HTTP Server, Routes, Database access, and more.

Welcome to DenoDeno

Installing Deno

Installing on Linux is simple:

curl -fsSL https://deno.land/install.sh | sh

Check verion with:

deno --version

Deno Project

Deno configuration file is deno.json which is similar to the package.json from Node.

It will automatically recognize this file in project root folder, but an arbitrary path to the configuration file can be passed through the --config flag when executing Deno.

Older versions of Deno used package.json as the configuration file, just like Node.

So, for backward compatibility it can work.

If both deno.json and package.json are present Deno will understand dependencies specified in both.

Use deno.json for Deno-specific configurations.

Also check more info in About.

deno.json

Check a full example of the configuration file here.

Dependencies

The "imports" field in your deno.json allows you to specify dependencies used in your project.

You can use it to map bare specifiers to URLs or file paths making it easier to manage dependencies and module resolution in your applications.

Tasks

The "tasks" field in your deno.json file is used to define custom commands that can be executed with the deno task command and allows you to tailor commands and permissions to the specific needs of your project. (Just like "scripts" from Node)

Linting

The "lint" field in the deno.json file is used to configure the behavior of Deno’s built-in linter.

This allows you to specify which files to include or exclude from linting, as well as customize the linting rules to suit your project’s needs.

Formatting

The "fmt" field in the deno.json file is used to configure the behavior of Deno’s built-in code formatter.

This allows you to customize how your code is formatted, ensuring consistency across your project, making it easier to read and collaborate on.

Read more about Deno default Linting and Formatting.

Say goodbye to Prettier.

Lockfile

The "lock" field in the deno.json file is used to specify configuration of the lock file that Deno uses to ensure the integrity of your dependencies.

You can disable Deno from creating the deno.lock file with:

deno.json

{
    "lock": false
}

Since Deno by default always add new added dependencies to the lockfile, it is also possible to freeze this lockfile (ex. CI pipelines or production environments) so that Deno will error when it encounter dependencies it's never seen before.

To do this you can pass the --frozen flag or add the configuration to deno.json.

{
    "lock": {
        "frozen": true
    }
}

Typescript compiler option

The "compilerOptions" field in the deno.json file is used to configure TypeScript compiler settings for your Deno project.

Include and Exclude properties

Many of the configurations in deno.json can accept include and exclude properties.

Check more detailed info on the docs.

Node and Npm Support

Node.js

Deno provides a compatibility layer that allows the use of Node.js built-in APIs within Deno programs.

However, in order to use them, you will need to add the node: specifier to any import statements that use them.

And run it with deno run main.mjs.

import * as os from "node:os";
console.log(os.cpus());

Npm

Deno has native support for importing npm packages by using npm: specifiers. For example:

import * as emoji from "npm:node-emoji";
console.log(emoji.emojify(`:sauropod: :heart:  npm`));

No npm install is necessary before the deno run command and no node_modules folder is created.

Importing types

Many npm packages ship with types, you can import these and use them with types directly:

import chalk from "npm:chalk@5";

Node to Deno Cheatcheat

Node.js	Deno
node file.js	deno file.js
ts-node file.ts	deno file.ts
nodemon	deno run --watch
node -e	deno eval
npm i / npm install	deno install
npm install -g	deno install -g
npm run	deno task
eslint	deno lint
prettier	deno fmt
package.json	deno.json or package.json
tsc	deno check
typedoc	deno doc
jest / ava / mocha / tap / etc	deno test
nexe / pkg	deno compile
npm explain	deno info
nvm / n / fnm	deno upgrade
tsserver	deno lsp
nyc / c8 / istanbul	deno coverage
benchmarks	deno bench

Examples

Bellow some examples on doing things with Deno.

Task
Files
Reading a text file (Deno.readTextFile)
Writing a text file (Deno.writeTextFile)
Reading files in streams
Network
Connect to the hostname and port (Deno.connect)
Announcing on the local transport address (Deno.listen)
Subprocess
Creating a subprocess (Deno.Command)
Error Handling
Deno error classes
Permissions
Check at TS level if a permission was given
Requesting permissions to User via CLI prompt
Revoking permissions at runtime
Storage
Using LocalStorage in Deno
Using WebWorkers in Deno
NodeJs Modules
Using node:crypto module
Using node:os module
Continuos Integration (CI)
Setting up a basic pipeline