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In Deno, applications are built using modules. Think of modules as individual files that contain related code, like functions, classes, or variables.

They help keep your code organized and reusable, preventing your project from becoming one giant, hard-to-manage file.

Unlike Node.js, Deno doesn't use a node_modules folder. Instead, Deno imports modules directly using URLs or file paths.

• Local Files: Use relative or absolute paths (e.g., ./my_module.ts).
• Remote Files: Use full URLs (e.g., https://deno.land/std/fs/mod.ts).

This simple approach makes dependency management very straightforward!

Let's create two files: utils.ts with a simple function, and main.ts to import and use it. This is how you share logic within your own project.

utils.ts:

Now, let's import and use our greet function in main.ts. Notice the relative path ./utils.ts.

Try running this example:

Deno can directly import modules from web URLs. This is powerful, but also requires trust in the source. Deno caches these modules after the first download.

Here's how to import a utility from Deno's standard library:

When you first run a Deno script that imports remote modules, Deno downloads and caches them locally. This makes subsequent runs much faster.

• Cached modules are stored in a global directory.
• You can manually clear the cache with deno cache --reload or deno cache --reset.
• Deno verifies module integrity using checksums.

Deno is designed to be secure. By default, a Deno program has no access to your file system, network, or environment variables.

You must explicitly grant these permissions using command-line flags when running your script. This prevents malicious code from doing harm without your knowledge.

To allow your Deno program to read files, you need the --allow-read permission. You can specify specific paths or allow access to everything with . (current directory) or by omitting a path.

data.txt:

Let's try to read data.txt. Without permission, it will fail. With --allow-read, it works! (e.g., deno run --allow-read main.ts)

Try running this example:

To allow your Deno program to make network requests (like fetching data from an API), you need the --allow-net permission.

You can specify specific hosts (e.g., --allow-net=api.example.com) or allow all network access. (e.g., deno run --allow-net main.ts)

Which of the following Deno commands would allow a script named app.ts to both read files from the current directory AND make network requests to any domain?

Great job! You've learned about Deno's modern module system, which uses URLs for both local and remote imports, simplifying dependency management.

You also explored Deno's robust permission model, understanding how to grant specific access (like --allow-read and --allow-net) to your scripts for secure execution. This "secure by default" approach is a core Deno feature!