Introduction to Deno: Practical Guide for Modern Development

Deno, created by Ryan Dahl (the same creator of Node.js), arrived as a secure and modern alternative to the traditional JavaScript runtime. Launched in 2020, Deno features native support for TypeScript, a restrictive permissions model, and a set of integrated tools (formatter, linter, test runner).

Why choose Deno?

Security by default, the process does not have access to files, network or environment without the developer explicitly granting it.
Native support for TypeScript, eliminates the need for external compilers.
ES-M Modules, imports via URLs simplify dependency management.
Integrated tools, deno fmt, deno lint and deno test come ready-made, reducing dependence on external packages.

Quick installation

curl -fsSL https://deno.land/x/install/install.sh | sh
## ou via Homebrew
brew install deno

The script adds the binary to $PATH.

Structure of a Deno project

A typical Deno project maintains a lean organization. At the root are deno.json, which defines permissions, import-map and lint options, and README.md. The source code goes under the directory src/, with the entry point at main.ts and the helper modules in files like utils.ts. The tests are isolated in tests/, following the convention of names with a suffix _test.ts, such as main_test.ts.

Permissions, the heart of security

When running a script, you must specify which resources it can access:

Permission	Description
`--allow-read`	Reading files or directories.
`--allow-write`	Writing to files or directories.
`--allow-net`	Network connections (HTTP, TCP, UDP).
`--allow-env`	Access to environment variables.
`--allow-run`	Execution of subprocesses.
`--allow-ffi`	Foreign Function Interface (C).

Safe execution example

deno run --allow-net src/main.ts

The script can make HTTP requests, but not read local files.

ES-M modules via URL

Deno allows you to import directly from public URLs:

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

The module is cached in ~/.deno and can be versioned via tag.

Creating a simple HTTP server

import { serve } from "https://deno.land/std@0.203.0/http/server.ts";

const handler = (request: Request): Response => {
  const url = new URL(request.url);
  if (url.pathname === "/") {
    return new Response("Olá Deno!", { status: 200 });
  }
  return new Response("Not Found", { status: 404 });
};

serve(handler, { port: 8000 });

The code above creates a server that responds Olá Deno! at the root.

Integrated tests

Deno includes a lightweight test runner:

denon test --allow-net tests/main_test.ts

The test may use assertEquals from the standard library.

Test example (3 lines)

import { assertEquals } from "https://deno.land/std@0.203.0/testing/asserts.ts";
Deno.test("soma", () => assertEquals(2 + 2, 4));

Deploy in production

Docker, official image denoland/deno simplifies deployment.

FROM denoland/deno:alpine-1.38.0
WORKDIR /app
COPY . .
RUN deno cache src/main.ts
EXPOSE 8000
CMD ["run", "--allow-net", "src/main.ts"]

Edge, Deno Deploy (service serverless) accepts scripts directly via URL.
CI/CD, GitHub Actions with deno lint && deno test && deno fmt --check guarantees quality.

Good security practices

Minimum permissions, grant only what is necessary (--allow-read=./data).
Lockfile, use deno lock to lock module versions.
Dependency audit, check external URLs before trusting.
Vulnerability scanning, tools like trivy can analyze the Docker image.

Quick checklist to start a Deno project

Install Deno (curl or brew).
Create deno.json with minimum permissions.
Structure directories (src, tests).
Write code using imports via URL.
Add unit tests.
Configure CI (lint, test, fmt).
Containerize with Docker or use Deno Deploy.
Review permissions before deployment.

Conclusion

Deno offers a secure, modern, and production-ready environment with fewer external dependencies. By adopting its restrictive permissions practices, ES-M modules, and integrated tools, developers can accelerate the delivery of robust applications and maintain a high standard of security.

What is your experience with Deno? Share in the comments!