How to Fetch Data from a Third-party API with Deno

This article explores Deno, a modern runtime environment designed as a potential successor or competitor to Node.js. Deno prioritizes security and offers built-in TypeScript support. We'll build a command-line tool that interacts with the Star Wars API to illustrate Deno's capabilities and highlight its key differences from Node.js.

We'll cover Deno's installation, environment setup, and the creation of a simple command-line application for making API requests. The accompanying code is available on GitHub.

Key Features of Deno:

• Enhanced Security: Deno operates within a secure sandbox, requiring explicit permissions for network access and file system interactions, unlike Node.js's default permissive approach.
• Built-in TypeScript: TypeScript support is integrated, eliminating the need for external configuration.
• ES Modules: Deno utilizes ES modules, foregoing CommonJS require statements.
• Built-in Code Formatter (deno fmt): Consistent code styling is ensured without relying on external tools.
• Top-Level Await: Cleaner asynchronous code is facilitated through top-level await support.
• Dependency Management: Third-party dependencies are imported directly via URLs, bypassing the need for a package manager. The Deno package repository serves as the primary source for libraries.

Installing Deno:

Detailed instructions are available on the official Deno website. For macOS/Linux, use:

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

Remember to update your $PATH environment variable. Windows users can leverage Chocolatey:

choco install deno

Alternative installation methods are listed on the deno_install page. Verify installation with:

deno -V

The Deno VS Code extension is highly recommended for VS Code users. Other editors may require specific plugins; consult the Deno documentation for guidance. For VS Code, enable the plugin via .vscode/settings.json:

{
  "deno.enable": true,
  "editor.formatOnSave": true,
  "editor.defaultFormatter": "denoland.vscode-deno"
}

Creating Your First Deno Script:

Create index.ts with the following:

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

Run using: deno run index.ts

Fetching Data with Deno:

Deno includes the Fetch API, eliminating the need for external packages. Let's make a request to the Star Wars API:

const response = await fetch("https://swapi.dev/api/people/1/");
const data = await response.json();
console.log(data);

Remember to grant network access using the --allow-net flag: deno run --allow-net=swapi.dev index.ts For enhanced security, specify the allowed domain: deno run --allow-net=swapi.dev index.ts

Managing Third-Party Dependencies:

To handle command-line arguments, we'll use Yargs. Import it directly from its URL:

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

Remember to pin the version number for better dependency management.

Using Yargs:

This snippet demonstrates how to use Yargs to parse command-line arguments:

choco install deno

Querying the Star Wars API and Output Enhancement:

The queryStarWarsAPI function fetches data, and helper functions (logFilms, logPeople, logPlanets) provide formatted output. Type definitions for Person, Film, and Planet improve type safety. The pluralise function handles singular/plural forms of "result".

Code Organization and Distribution:

Refactor the code by moving API-related logic to api.ts and importing it into index.ts. Use deno bundle index.ts out.js to create a single JavaScript file for easy distribution. For a self-contained executable (experimental), use deno compile --unstable --allow-net=swapi.dev index.ts.

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