Learn Deno: A Secure JavaScript & TypeScript Runtime

Deno 1.0, released in May 2020, has generated significant interest. This article provides a comprehensive overview of Deno, its key features, and reasons for its growing popularity.

Key Features & Benefits:

Deno, a JavaScript and TypeScript runtime environment created by Ryan Dahl (also the creator of Node.js), aims to rectify perceived Node.js design flaws. Its core strengths include default security, native TypeScript support, and enhanced browser compatibility. Deno prioritizes security by executing code within a secure sandbox, demanding explicit permissions for network or file system access. TypeScript is a first-class citizen, eliminating the need for separate compilation steps. Unlike Node.js's npm or PHP's Composer, Deno eschews a traditional package manager, instead importing modules directly via URLs. A comprehensive standard library offers various tools for building command-line and HTTP applications.

What is Deno?

Deno serves as a runtime for executing JavaScript and TypeScript code directly from the command line. Unlike browser-based JavaScript, Deno programs can interact with host computer resources like the file system and environment variables. Its creation stemmed from Dahl's desire to improve upon Node.js's design, focusing on security, TypeScript integration, and browser compatibility.

Security:

Deno's security is paramount. Its sandboxed execution model necessitates explicit permission grants for accessing network resources or the file system. Command-line flags control these permissions: -A (allow all – disables security), --allow-env (environment variables), --allow-hrtime (high-resolution time), --allow-net (network access, optionally whitelisting domains), --allow-plugin (plugins – unstable), --allow-read (file system read access, with optional directory/file whitelisting), --allow-run (subprocesses), and --allow-write (file system write access, with optional whitelisting).

TypeScript Support:

Deno seamlessly supports both JavaScript and TypeScript. TypeScript is treated as a first-class language, enabling direct execution without pre-compilation. This simplifies development workflows.

External Code Handling:

Deno avoids a dedicated package manager. External packages are imported using URLs:

import { Client } from "https://deno.land/x/mysql@2.2.0/mod.ts";

Initial execution fetches, compiles, and caches imports for subsequent speed. The deno cache --reload my_module.ts command forces re-fetching. While lacking a central registry, a list of third-party modules is available, often linked to GitHub repositories.

Standard Library:

Deno boasts a robust standard library (similar to Golang's), offering numerous modules without external dependencies. These modules are accessed via versioned URLs:

import { Client } from "https://deno.land/x/mysql@2.2.0/mod.ts";

This ensures code compatibility across library versions. Modules include tools for archives, asynchronous operations, binary data handling, date/time manipulation, encoding/decoding, command-line argument parsing, formatted output, file system interaction, hashing, HTTP operations, input/output, logging, MIME types, Node.js compatibility (in progress), path manipulation, permission checks, signal handling, testing, UUIDs, and WebSockets.

Installation & Upgrades:

Deno is a single executable, installable via various methods:

• Shell (macOS/Linux): curl -fsSL https://deno.land/x/install/install.sh | sh
• PowerShell (Windows): iwr https://deno.land/x/install/install.ps1 -useb | iex
• Homebrew (macOS): brew install deno

Upgrades are performed using deno upgrade or specifying a version: deno upgrade --version 1.0.1.

Future Prospects:

Deno is a compelling alternative for utility scripts previously written in Bash or Python. Its adoption is expected to grow in areas currently dominated by Node.js, with emerging frameworks for building REST APIs and a continuously expanding ecosystem of third-party modules. While Node.js remains relevant, Deno is a technology worth monitoring.

Further Learning:

A comprehensive collection of Deno resources, including fundamentals (guides, comparisons with Node.js, built-in tools, module system, API interaction, file system operations) and projects (microservices, command-line weather app), is available.

Frequently Asked Questions:

• What is Deno? A secure, modern JavaScript/TypeScript runtime for executing code outside web browsers.
• How does Deno differ from Node.js? Deno emphasizes security, built-in TypeScript support, a standard library, and URL-based module imports, unlike Node.js's npm.
• Can I run Node.js modules in Deno? Not directly, but tools like denoify offer partial compatibility.
• Does Deno support TypeScript? Yes, natively.
• How does Deno handle security? Through permission-based access control and sandboxed execution.

This detailed explanation provides a comprehensive understanding of Deno and its capabilities.

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