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# Introduction
Deno is a JavaScript/TypeScript runtime with secure defaults and a great
developer experience.
It's built on V8, Rust, and Tokio.
## Feature highlights
- Secure by default. No file, network, or environment access (unless explicitly
enabled).
- Supports TypeScript out of the box.
- Ships a single executable (`deno`).
- Has built-in utilities like a dependency inspector (`deno info`) and a code
formatter (`deno fmt`).
- Has
[a set of reviewed (audited) standard
modules](https://github.com/denoland/deno/tree/master/std) that are guaranteed
to work with Deno.
- Scripts can be bundled into a single JavaScript file.
## Philosophy
Deno aims to be a productive and secure scripting environment 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 ~15 megabyte zipped executable](https://github.com/denoland/deno/releases).
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
- Only ship 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.
- Not leak V8 concepts into user land.
- Serve HTTP efficiently.
## Comparison to Node.js
- Deno does not use `npm`.
- It uses modules referenced as URLs or file paths.
- Deno does not use `package.json` in its module resolution algorithm.
- All async actions in Deno return a promise. Thus Deno provides different APIs
than Node.
- Deno requires explicit permissions for file, network, and environment access.
- Deno always dies on uncaught errors.
- Uses "ES Modules" and does not support `require()`. Third party modules are
imported via URLs:
```javascript
import * as log from "https://deno.land/std@$STD_VERSION/log/mod.ts";
```
## Other key behaviors
- Remote code is fetched and cached on first execution, and never updated 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.
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