Deno

Installation and Setup

Deno is installed once per machine. On macOS and Linux, Deno’s documentation recommends the official install script:

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

On Windows, run this in PowerShell:

PS> irm https://deno.land/install.ps1 | iex

Next, confirm the installed version:

$ deno --version
deno 2.9.8 (stable, release, x86_64-unknown-linux-gnu)
v8 15.0.245.2-rusty
typescript 6.0.3

Key Features

• Runs .ts files directly, without a separate build step.
• Blocks file, network, and environment access unless flags such as --allow-read or --allow-net grant it.
• Imports npm packages through npm: specifiers and runs existing projects that use package.json.
• Formats, lints, and tests code with the built-in deno fmt, deno lint, and deno test commands.
• Runs named scripts from the tasks field in deno.json with deno task.

Usage

Say a shop’s cart.ts script reads its items from a prices.json file and logs the order total. The --allow-read flag grants read access, so the script runs:

$ deno run --allow-read cart.ts
Total: 22.5

Without the flag, Deno asks for permission in an interactive terminal. When access is refused, the read throws a NotCapable error.

The init command creates a new project with a deno.json config file, a main.ts module, and a main_test.ts test file:

$ deno init shop

Inside the project folder, the test command type-checks and runs every test file:

$ deno test
Check main_test.ts
running 2 tests from ./main_test.ts
returns html on / ... ok (9ms)
returns json on /api ... ok (644µs)

ok | 2 passed | 0 failed (18ms)

The tasks field in deno.json gives longer commands a short name:

{
  "tasks": {
    "dev": "deno run --watch --allow-net main.ts"
  }
}

With that task defined, deno task dev starts the server and restarts it when a file changes:

$ deno task dev

The fmt and lint commands format and check every file in the project:

$ deno fmt
$ deno lint

For every command and flag, see the Deno documentation.

Related Resources

Tutorial

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