Getting Started with Deno: A Secure Runtime for JavaScript and TypeScript

by Hexagon, , Updated: 6 minutes read deno javascript typescript security npm denokv

If you're into JavaScript or TypeScript, you've probably heard about Deno. It's an exciting new runtime that's often described as a more secure and simpler alternative to Node.js. In this blog post, we'll go over what makes Deno awesome and how to get started.



Table of Contents

  1. Why Deno?
  2. How to Install
  3. Hello Deno!
  4. Importing Packages
  5. Quick Guide to Deno’s CLI
  6. Configuring Deno with deno.json
  7. Deno Best Practices
  8. Looking Ahead: Deno 2.0
  9. Deno resources
  10. Wrapping Up

Why Deno?

Security First

One of Deno's biggest selling points is its focus on security. Unlike Node.js and Bun, where you have to manually restrict permissions, Deno is secure by default. That means no random package can mess with your system unless you give it the OK.

For example, to run main.ts and allow it to access api.openai.com, you'd run:

deno run --allow-net=api.openai.com main.ts

Simplicity

Deno keeps things simple. You don't need to deal with complex configs or install a bunch of extra stuff to get going. Write your code in JavaScript or TypeScript, and Deno takes care of the rest. Out of the box, it supports TypeScript, code formatting, linting, type checking, and even compiling your code to a binary.

Built-in Key/Value store

It has a built-in Key/Value-store, which allows you to access a JavaScript friendly database with only a few lines of code. In custom deployments, it's based on SQLite, if using Deno Deploy, it uses a cloud based store.

Backwards Compatible

One of the cool things about Deno is that it's backwards compatible with npm packages. This means you can still use all those npm libraries you know and love. For those who don't want to be weighed down by what's known as the heaviest object in the universe (node_modules), there is an --no-npm flag.

For those interested in diving deeper into how Deno measures up against other runtimes, I've provided comprehensive comparisons in my articles: Deno vs. Bun vs. Node.js: A Feature Comparison and Deno vs. Bun vs. Node.js: A Speed Comparison.

How to Install

Installing Deno is a breeze:

Using Shell (macOS and Linux):

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

Using PowerShell (Windows):

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

If you prefer other ways to install, check out the official documentation.

Hello Deno!

You don't need to install anything else to start writing Deno apps. Open a text editor, create a new .ts or .js file, and you're good to go!

For example, create a hello.ts file and write:

console.log("Hello, Deno!");

Run your program with deno run hello.ts. You should see the output "Hello, Deno!"

If you're new to JavaScript (or TypeScript for that matter), consider checking out The Guide to JavaScript covering everything from the basics to advanced topics.

Importing Packages

Deno can use any JavaScript/TypeScript module simply by importing them directly from an url, and has its own package register at deno.land/x.

Let's take a basic example:

import { Cron } from "https://deno.land/x/croner@7.0.1/dist/croner.js";

// Run a function at the interval defined by a cron expression
const job = Cron("*/5 * * * * *", () => {
  console.log("This will run every fifth second");
});

Deno can also use popular npm packages not yet available natively to Deno through the npm:-specifier:

// @deno-types="npm:@types/express@4.17.15"
import express from "npm:express@4.18.2";

const app = express();

app.get("/", (req, res) => {
  res.send("Hello Express!");
});

app.listen(8000);

Quick Guide to Deno’s CLI

Deno comes with a set of powerful command-line tools that allow developers to easily run scripts, manage dependencies, and more. Below are some commonly used Deno commands that can help you get started.

Running Scripts

To run a script, use the deno run command followed by the name of your script.

deno run hello.ts

Managing Permissions

Deno is secure by default, which means scripts run in a sandbox environment. For any external access, such as network, file, and environment access, explicit permissions are required. To allow network access, for example, use the --allow-net flag:

deno run --allow-net=example.com myscript.ts

If you want to give Deno all permissions, you can use -A:

deno run -A myscript.ts

Formatting Code

Deno provides a built-in code formatter that helps keep your codebase consistent. To format your code, use the deno fmt command followed by the name of your script or directory:

deno fmt myfile.ts

Type Checking and Linting

Deno’s built-in tools also include a type checker and a linter to help you catch errors early and enforce code quality. To check types in your script, run:

deno check myfile.ts

And to lint your code, use:

deno lint myfile.ts

Bundling and Compiling

Deno also allows you to bundle and compile your TypeScript or JavaScript code easily with the deno bundle and deno compile commands, respectively:

deno bundle myscript.ts output.bundle.js

deno compile myscript.ts

Viewing Documentation

If you ever need a quick reference for the APIs and modules in your code, you can generate documentation using the deno doc command:

deno doc mymodule.ts

Installing Scripts

Deno enables you to install scripts as executables using the deno install command. It’s great for creating CLI tools:

deno install -n mycli myscript.ts

Explore the official documentation for more advanced use cases and additional information.

Configuring Deno with deno.json

Deno allows configuration of project settings through a deno.json or deno.jsonc file. This configuration file, placed at the root of your project, is instrumental in defining various project-level settings, such as compiler options and lint rules.

Here is an example of a basic deno.json file:

{
  "compilerOptions": {
    "lib": ["deno.ns", "dom"],
    "strict": true
  },
  "lint": {
    "rules": {
      "tags": ["recommended"]
    }
  }
}

This configuration file specifies compiler options such as which libraries to include (deno.ns and dom) and whether to enforce strict type checking ("strict": true). It also sets up linting rules, including all recommended rules.

Why is deno.json Important?

Having a deno.json file in your project allows you to maintain consistent settings across your development environment. It’s crucial for defining how Deno should behave when running, linting, or bundling your code, and can be used to set up specific permissions or environment variables that your project needs to run correctly.

Remember to consult the official documentation to understand all the available configuration options and to set up the deno.json file according to your project needs.

Deno Best Practices

Developing with Deno can be a breeze, but to ensure the maintainability, scalability, and robustness of your codebase, following best practices is essential.

Explicitly Specify Permissions

Always specify the permissions needed for your Deno scripts explicitly, rather than running scripts with the -A flag which gives full permissions. This mitigates security risks by adhering to the principle of least privilege.

deno run --allow-read --allow-net myscript.ts

Utilize TypeScript

Take advantage of Deno’s built-in TypeScript support. TypeScript helps catch errors early, enhances code quality, and improves developer experience through static typing.

Keep Dependencies Up To Date

Regularly update the dependencies in your project to the latest versions to benefit from bug fixes, new features, and security updates. But, always test your application thoroughly after updating to ensure everything works as expected.

Write Tests

Writing tests is crucial for maintaining a healthy codebase. Deno provides a built-in test runner, making it easy to write and run tests for your application.

deno test

Use Built-in Tooling

Leverage Deno’s built-in tools for formatting, linting, testing, bundling, and compiling your codebase, ensuring a consistent and error-free development experience.

deno fmt
deno lint
deno test
deno bundle
deno compile

Prefer Deno Standard Library

When possible, prefer using modules from the Deno standard library as they are well-maintained, tested, and optimized for Deno.

Looking Ahead: Deno 2.0

There's a lot of chatter about Deno 2.0, which is rumored to be coming out later this year. I can't wait to see what new features and improvements it'll bring.

Deno resources

If you're looking for inspiration, you can check out some other write ups on Deno:

Other good Deno resources to check out:

Wrapping Up

So that's it! You now know how to get started with Deno. It's a simpler, more secure alternative to Node.js and has some cool features like a built-in key-value store and npm compatibility. With Deno 2.0 on the horizon, it's a great time to get on board.

Deno vs. Bun vs. Node.js: A Feature Comparison Show All Visitor's Pointers on a Webpage