# Beginner's Guide to Deno

So you want to learn about Deno, the new JavaScript runtime? Well, you've come to the right place! This guide will teach you everything you need to know about Deno.

## What is Deno?

Deno is a runtime for JavaScript, TypeScript, and WebAssembly that is based on the V8 JavaScript engine and the Rust programming language. It was created by Ryan Dahl, the original creator of Node.js, to remedy some the regrets he had when making Node.

## Why Should I Use Deno?

Here are a few reasons why you might want to use Deno:

1. Secure by default. This means that it uses a sandbox to prevent code execution from outside the Deno process, and all network and file system operations are sandboxed by default.

2. Built-in support for TypeScript.

2. Ships with a set of standard libraries, which are written in TypeScript and are located in the Deno namespace. This means that you don't have to install third-party libraries to use Deno.

3. A plugin system that allows you to import third-party libraries as plugins. This means that you can import only the functionality that you need, and the plugin is sandboxed and can't access the Deno process.

4. A built-in test runner, which makes it easy to write and run tests for your Deno applications.

5. Open source and released under the MIT License.

## Getting Started

Now that you know a little bit about Deno, let's get started!

First, you need to install Deno. The easiest way to do this is in with curl:

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

If you're on Mac, you can install Deno with a package manager like [Homebrew](https://brew.sh/).

```zsh
brew install deno
```

Now that you have Deno installed, you can run Deno programs with the `deno` command.

```zsh
deno run https://deno.land/std/examples/cat.ts
```

This will fetch and run the `cat.ts` program from the [Deno Standard Library](https://deno.land/std/). The Deno Standard Library contains a collection of reusable Deno programs.

Now that you know how to run Deno programs, let's write our own! Create a file called `hello.ts` and add the following code to it:

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

You can run this program with the `deno` command:

```bash
deno run hello.ts
```

You should see the output `Hello, world!`.

That's it! You've written your first Deno program!


## Writing Deno Programs

Now that you know the basics of Deno, let's dive a bit deeper. In this section, we'll learn about some of the more advanced concepts in Deno.

### Scripts and Modules

In Deno, there are two ways to structure your code: scripts and modules.

Scripts are simple programs that are run with the `deno` command. Modules are program modules that can be imported by other programs.

Let's see an example of each.

First, let's create a script. Create a file called `script.ts` and add the following code to it:

```typescript
console.log("This is a script.");
```

You can run this script with the `deno` command:

```bash
deno run script.ts
```

Next, let's create a module. Create a file called `module.ts` and add the following code to it:

```typescript
export function hello() {
  console.log("Hello, world!");
}
```

This module exports a single function called `hello`. We can import this function into another program and call it.

Create a file called `main.ts` and add the following code to it:

```typescript
import { hello } from "./module.ts";

hello();
```

This program imports the `hello` function from the `module.ts` module and calls it.

You can run this program with the `deno` command:

```bash
deno run main.ts
```

You should see the output `Hello, world!`.

### Libraries

In Deno, libraries are collections of modules that are bundled together. Libraries can be published to [Deno's Registry](https://deno.land/x) so that they can be easily reused by others.

Let's see an example of how to use a library. We're going to use the [gravatar](https://deno.land/x/gravatar/) library to generate Gravatar URLs.

Create a file called `main.ts` and add the following code to it:

```typescript
import { gravatar } from "https://deno.land/x/gravatar/mod.ts";

console.log(gravatar("example@example.com"));
```

This program imports the `gravatar` function from the `gravatar` library and calls it with the email address `example@example.com`.

You can run this program with the `deno` command:

```bash
deno run main.ts
```

You should see the output `https://www.gravatar.com/avatar/00000000000000000000000000000000?d=mp&s=80`.

## Conclusion

You should now have a good understanding of Deno and be able to start writing your own programs. For more information, check out the [Deno documentation](https://deno.land/manual).

Let me know in the comments if this was helpful or if you have any questions.

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