introduction.md

Introduction

Deno (/ˈdiːnoʊ/, pronounced dee-no) is a JavaScript, TypeScript, and WebAssembly runtime with secure defaults and a great developer experience.

It's built on V8, Rust, and Tokio.

Feature highlights

• Provides web platform functionality and adopts web platform standards. For example using ES modules, web workers, and support fetch().
• Secure by default. No file, network, or environment access unless explicitly enabled.
• Supports TypeScript out of the box.
• Ships a single executable (deno).
• Provides built-in development tooling like a code formatter (deno fmt), a linter (deno lint), a test runner (deno test), and a language server for your editor.
• Has a set of reviewed (audited) standard modules that are guaranteed to work with Deno.
• Supports the use of existing npm modules

Philosophy

Deno aims to be a productive, secure, and performant runtime for the modern programmer.

Deno will always be distributed as a single executable. Given a URL to a Deno program, it is runnable with nothing more than the ~31 megabyte zipped executable. Deno explicitly takes on the role of both runtime and package manager. It uses a standard browser-compatible protocol for loading modules: URLs.

Among other things, Deno is a great replacement for utility scripts that may have been historically written with Bash or Python.

Goals

• Ship as just a single executable (deno).
• Provide secure defaults.
  • Unless specifically allowed, scripts can't access files, the environment, or the network.
• Be browser-compatible.
  • The subset of Deno programs which are written completely in JavaScript and do not use the global Deno namespace (or feature test for it), ought to also be able to be run in a modern web browser without change.
• Provide built-in tooling to improve developer experience.
  • E.g. unit testing, code formatting, and linting.
• Keep V8 concepts out of user land.
• Serve HTTP efficiently.

Other key behaviors

• Fetch and cache remote code upon first execution, and never update it until the code is run with the --reload flag. (So, this will still work on an airplane.)
• Modules/files loaded from remote URLs are intended to be immutable and cacheable.