# TypeScript Basics

TypeScript is a strongly typed programming language that builds on JavaScript, giving you better tooling at any scale. It is a strict superset of JavaScript, meaning any valid JavaScript code is also valid TypeScript code. The key addition is **static typing**.

## Why TypeScript?

*   **Catch Errors Early:** Types allow you to catch bugs at compile time rather than runtime.
*   **Better Tooling:** IDEs (like VS Code) provide excellent autocompletion, navigation, and refactoring support.
*   **Readability:** Type definitions serve as documentation for your code.

## 1. Installation

You can install TypeScript globally or as a dependency in your project using npm (Node Package Manager).

### Global Installation

```bash
npm install -g typescript
```

Verify the installation:

```bash
tsc --version
```

### Local Installation (Recommended for Projects)

```bash
npm install typescript --save-dev
```

## 2. Basic Usage

### Creating a TypeScript File

Create a file named `hello.ts`.

```typescript
function greet(person: string, date: Date) {
  console.log(`Hello ${person}, today is ${date.toDateString()}!`);
}

greet("Brendan", new Date());
```

Notice the type annotations (`: string`, `: Date`). If you try to pass a number to `person`, TypeScript will throw an error.

### Compiling to JavaScript

Browsers and Node.js cannot execute TypeScript directly. You must compile (transpile) it to JavaScript using the TypeScript Compiler (`tsc`).

```bash
tsc hello.ts
```

This generates a `hello.js` file in the same directory, which you can run with Node.js or include in an HTML file.

```bash
node hello.js
```

## 3. Configuration (`tsconfig.json`)

For real projects, you don't want to run `tsc filename.ts` manually every time. You use a configuration file.

Initialize a configuration file:

```bash
tsc --init
```

This creates `tsconfig.json`. Common settings include:

```json
{
  "compilerOptions": {
    "target": "es2016",                                  /* Set the JavaScript language version for emitted JavaScript. */
    "module": "commonjs",                                /* Specify what module code is generated. */
    "rootDir": "./src",                                  /* Specify the root folder within your source files. */
    "outDir": "./dist",                                  /* Specify an output folder for all emitted files. */
    "strict": true,                                      /* Enable all strict type-checking options. */
    "esModuleInterop": true                              /* Emit additional JavaScript to ease support for importing CommonJS modules. */
  }
}
```

Now, you can simply run `tsc` in your terminal, and it will compile all files in `src` to `dist` based on these rules.

## 4. Basic Types

```typescript
// Primitives
let isDone: boolean = false;
let decimal: number = 6;
let color: string = "blue";

// Arrays
let list: number[] = [1, 2, 3];
let listGeneric: Array<number> = [1, 2, 3];

// Tuples (Fixed length array with known types)
let x: [string, number];
x = ["hello", 10];

// Enums
enum Color {Red, Green, Blue}
let c: Color = Color.Green;

// Any (Opt-out of type checking)
let notSure: any = 4;
notSure = "maybe a string instead";

// Void (No return value)
function warnUser(): void {
    console.log("This is my warning message");
}
```

[[programming/javascript/javascript]]