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## What is `tsconfig.json`

`tsconfig.json` is a **JSON file** that describes exactly how the TypeScript compiler (`tsc`) should work with the project.

Example of a minimal file:

```javascript
{
  "compilerOptions": {
    "target": "ES2020",
    "module": "commonjs",
    "strict": true,
    "outDir": "dist"
  },
  "include": ["src"]
}
```

---

## Main purpose

The `tsconfig.json` file is responsible for:

1. **Compilation settings** (`compilerOptions`);
2. **Paths to source files** (`include` / `exclude`);
3. **Project structure** (references, extends, composite);
4. **Strict typing mode**;
5. **Output directories and module formats**.

---

## 1. Main sections

### `compilerOptions`

The main section. It specifies the compiler parameters:

| Option | Description |
| --- | --- |
| `"target"` | Which JS version to compile to (ES5, ES6, ES2020, ESNext) |
| `"module"` | Module system (`commonjs`, `esnext`, `amd`) |
| `"outDir"` | Where to save the compiled `.js` files |
| `"rootDir"` | Where to look for sources (usually `src`) |
| `"strict"` | Enables all strict type checks |
| `"esModuleInterop"` | Simplifies importing CommonJS modules |
| `"skipLibCheck"` | Skips type checking in dependencies |
| `"sourceMap"` | Creates `.map` files for debugging |

Example:

```javascript
"compilerOptions": {
  "target": "ES2020",
  "module": "ESNext",
  "rootDir": "src",
  "outDir": "dist",
  "strict": true,
  "esModuleInterop": true,
  "sourceMap": true
}
```

---

### `include` and `exclude`

Specify **which files** to compile.

```javascript
"include": ["src/**/*"],
"exclude": ["node_modules", "dist"]
```

> This helps avoid unnecessary compilation of service files.

---

### `extends`

Allows you to **inherit settings** from another `tsconfig.json`.
Useful in a monorepo or when separating frontend and backend.

```javascript
{
  "extends": "../../tsconfig.base.json",
  "compilerOptions": {
    "outDir": "build"
  }
}
```

---

## Where `tsconfig.json` should be located

Usually - **at the project root**, next to `package.json`.

Example structure:

```javascript
my-project/
├── src/
│   ├── index.ts
│   ├── utils/
│   └── components/
├── dist/
├── package.json
└── tsconfig.json
```

> This way the `tsc` compiler will by default **find this file on its own** when you simply run:

```javascript
npx tsc
```

---

## Additionally

### You can have several configs

For example, one for development, another for the build:

```javascript
tsconfig.json          // general
tsconfig.build.json    // for production
```

In `tsconfig.build.json` you can disable source maps and test files:

```javascript
{
  "extends": "./tsconfig.json",
  "exclude": ["**/*.test.ts", "src/dev-tools"]
}
```

---

## Summary

> `tsconfig.json` is the file where you describe
> exactly how TypeScript should compile the project:
> which files to take, which standards and modules to use,
> where to put the output, and which checks to enable.

**Located at the project root**, so the compiler finds it automatically.

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