Deno 2 7 0

Deno 2.7

Overview

Deno (pronounced dee-no) is an open-source JavaScript, TypeScript, and WebAssembly runtime built on V8, Rust, and Tokio. It provides secure defaults, first-class TypeScript support, a robust built-in toolchain, and full Node.js/npm compatibility. Deno 2.x represents the current major version with enhanced performance, improved npm integration, and workspace support.

Key features:

• TypeScript-ready out of the box — zero config needed
• Secure by default — no filesystem, network, or environment access without explicit permission
• Built-in toolchain — test runner, linter, formatter, bundle, compile
• Node.js and npm compatible — import npm packages with npm: specifiers
• JSR integration — first-party package registry at jsr.io
• Standard library — modular @std packages published on JSR

When to Use

• Building JavaScript/TypeScript applications with a modern, secure runtime
• Migrating Node.js projects to Deno (full npm compatibility)
• Writing CLI tools, HTTP servers, or scripts with built-in tooling
• Working with TypeScript without separate compilation steps
• Deploying serverless applications to Deno Deploy
• Managing monorepo projects with workspace support
• Needing a batteries-included runtime with no external dependencies

Core Concepts

Permissions model: Deno denies all I/O by default. Use --allow-read, --allow-write, --allow-net, --allow-env, and --allow-run flags to grant access. Permissions can also be configured in deno.json.

Module specifiers: Deno supports multiple import sources:

• Local files: import { x } from "./module.ts"
• URLs: import { x } from "https://esm.sh/..."
• JSR packages: import { x } from "jsr:@std/assert@^1.0.0"
• npm packages: import { x } from "npm:chalk@5"
• Node built-ins: import fs from "node:fs"

Configuration: The deno.json (or deno.jsonc) file configures imports, tasks, linting, formatting, permissions, and TypeScript compiler options. Deno also supports package.json for Node.js compatibility.

Standard library: Published as modular @std packages on JSR. Key packages include @std/assert, @std/fs, @std/http, @std/path, @std/async, and many more.

Installation / Setup

Install Deno using the official install script:

# macOS and Linux
curl -fsSL https://deno.land/install.sh | sh

# Windows (PowerShell)
irm https://deno.land/install.ps1 | iex

Verify installation:

deno --version

Additional installation options include package managers (Homebrew, Chocolatey, npm), binary downloads from GitHub releases, and APT/YUM repositories → Installation for details.

Usage Examples

Hello World server:

Deno.serve((_req) => {
  return new Response("Hello, World!");
});

Run with: deno run --allow-net server.ts

Import an npm package:

import chalk from "npm:chalk@5";
console.log(chalk.green("Hello from npm in Deno"));

Using the standard library:

import { assertEquals } from "jsr:@std/assert";
import { walk } from "jsr:@std/fs/walk";

// Walk a directory
for await (const entry of walk("./src")) {
  console.log(entry.path);
}

Configuration with bare specifiers:

// deno.json
{
  "imports": {
    "@std/assert": "jsr:@std/assert@^1.0.0",
    "chalk": "npm:chalk@5"
  },
  "tasks": {
    "start": "deno run --allow-net server.ts",
    "test": "deno test --allow-read",
    "lint": "deno lint"
  }
}

// Now use bare specifiers
import { assertEquals } from "@std/assert";
import chalk from "chalk";

Advanced Topics

Permissions and Security: Granular permission flags, deny rules, configuration file permissions → Security

Node.js and npm Compatibility: Importing npm packages, CommonJS support, node: built-ins, node_modules management → Node Compatibility

Configuration (deno.json): Tasks, imports, lint/fmt settings, lockfile, TypeScript options, publish config → Configuration

Testing and Benchmarking: Built-in test runner, hooks, coverage, snapshot testing, BDD → Testing

HTTP Server and Web Development: Deno.serve, HTTP/2, HTTPS, WebSockets, file serving → HTTP Server

Workspaces and Monorepos: Multi-package management, path patterns, publishing → Workspaces

FFI (Foreign Function Interface): Calling native C/Rust libraries, type mapping, callbacks → FFI

CLI Reference: Complete subcommand reference for deno run, test, lint, fmt, compile, publish, etc. → CLI Reference

Standard Library (@std): Overview of all @std packages on JSR → Standard Library

Deployment: Deno Deploy platform, deno deploy CLI, Deno KV database → Deployment

Debugging and Profiling: Chrome DevTools integration, CPU profiling, inspect flags → Debugging