How to Get Started with Deno: A Beginner's Guide

JavaScript and TypeScript developers have long relied on Node.js for server-side programming. However, a new runtime environment, Deno, has emerged as a modern alternative. Created by Ryan Dahl, the original creator of Node.js, Deno addresses many of the shortcomings of its predecessor, offering a more secure, streamlined, and developer-friendly experience.

If you're curious about Deno and want to get started, this beginner's guide will walk you through the basics, from installation to running your first Deno application.

---

What is Deno?

Deno is a modern runtime for JavaScript and TypeScript that runs on the V8 engine, the same engine that powers Google Chrome. Unlike Node.js, Deno is designed with security, simplicity, and developer productivity in mind. Here are some of its standout features:

• Built-in TypeScript support: No need for additional configuration or compilers.
• Secure by default: Deno restricts file, network, and environment access unless explicitly allowed.
• Single executable: Deno is distributed as a single binary, making installation and updates straightforward.
• Standard library: Comes with a robust standard library, reducing the need for third-party dependencies.
• Modern ES module support: Uses ES modules instead of CommonJS, aligning with modern JavaScript standards.

---

Why Choose Deno?

Deno is an excellent choice for developers who want a fresh, modern approach to server-side JavaScript and TypeScript. Here are a few reasons to consider Deno:

1. Security: Unlike Node.js, Deno requires explicit permissions for accessing files, the network, or the environment, reducing the risk of vulnerabilities.
2. TypeScript-first: Deno has built-in TypeScript support, eliminating the need for additional tools like ts-node or babel.
3. Simplified dependency management: Deno uses URLs to import modules, removing the need for a package.json file or a node_modules directory.
4. Active development: As a newer runtime, Deno is actively evolving, with a focus on modern development practices.

---

Step 1: Installing Deno

Installing Deno is quick and easy. It’s distributed as a single executable, so you can install it using your preferred method:

Using Shell (Linux/macOS):

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

Using Homebrew (macOS):

brew install deno

Using Chocolatey (Windows):

choco install deno

Using Scoop (Windows):

scoop install deno

Once installed, verify the installation by running:

deno --version

This command will display the installed version of Deno, confirming that it’s ready to use.

---

Step 2: Running Your First Deno Script

Let’s create a simple Deno script to get familiar with the runtime. Follow these steps:

1. Create a new file called hello.ts:

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

2. Run the script using the Deno CLI:

   deno run hello.ts
   

   You should see the output:

   Hello, Deno!
   

Congratulations! You’ve just run your first Deno script.

---

Step 3: Understanding Permissions in Deno

One of Deno’s key features is its security model. By default, Deno scripts cannot access the file system, network, or environment variables without explicit permissions. Let’s explore how this works.

Example: Reading a File

Create a file called example.txt with the following content:

This is a test file.

Now, create a script called readFile.ts:

const decoder = new TextDecoder("utf-8");
const data = await Deno.readFile("example.txt");
console.log(decoder.decode(data));

Run the script with the --allow-read flag to grant file system access:

deno run --allow-read readFile.ts

Without the --allow-read flag, Deno will throw a permission error, demonstrating its secure-by-default approach.

---

Step 4: Using Deno’s Standard Library

Deno comes with a built-in standard library that includes utilities for working with files, HTTP servers, and more. Let’s create a simple HTTP server using the standard library.

Create a file called server.ts:

import { serve } from "https://deno.land/[email protected]/http/server.ts";

const handler = (request: Request): Response => {
  return new Response("Hello, Deno!");
};

console.log("HTTP server is running on http://localhost:8000");
serve(handler, { port: 8000 });

Run the server with the --allow-net flag to grant network access:

deno run --allow-net server.ts

Visit http://localhost:8000 in your browser, and you’ll see the message: Hello, Deno!.

---

Step 5: Managing Dependencies

Deno uses URLs to import external modules, eliminating the need for a package.json file or a node_modules directory. For example:

import { serve } from "https://deno.land/[email protected]/http/server.ts";

To manage dependencies more effectively, you can use an import_map.json file. Here’s an example:

1. Create an import_map.json file:

   {
     "imports": {
       "http/": "https://deno.land/[email protected]/http/"
     }
   }
   

2. Update your script to use the import map:

   import { serve } from "http/server.ts";
   

3. Run the script with the --import-map flag:

   deno run --allow-net --import-map=import_map.json server.ts
   

This approach makes it easier to manage and update dependencies.

---

Step 6: Exploring Deno Deploy

Deno Deploy is a cloud platform for deploying Deno applications. It’s fast, scalable, and requires no additional configuration. To get started, visit Deno Deploy and follow the setup instructions.

---

Conclusion

Deno is a powerful and modern runtime for JavaScript and TypeScript, offering a secure and developer-friendly alternative to Node.js. With its built-in TypeScript support, robust standard library, and focus on security, Deno is an excellent choice for building modern web applications.

By following this guide, you’ve learned how to install Deno, run your first script, work with permissions, and create a simple HTTP server. As you continue exploring Deno, you’ll discover even more features and capabilities that make it a compelling tool for developers.

Ready to dive deeper? Check out the official Deno documentation for more advanced topics and examples. Happy coding!