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## 1. A simple array of primitives

### Syntax 1 - via `type[]`

```javascript
const numbers: number[] = [1, 2, 3, 4];
const names: string[] = ["Tim", "Max", "Bob"];
```

> The most common and convenient way is `type[]`.

---

### Syntax 2 - via the `Array<type>` generic

```javascript
const numbers: Array<number> = [1, 2, 3, 4];
const names: Array<string> = ["Tim", "Max", "Bob"];
```

> Fully equivalent to `number[]`,
> just a different notation (useful when the inner type is complex).

---

## 2. An array of objects

```javascript
interface User {
  id: number;
  name: string;
}

const users: User[] = [
  { id: 1, name: "Tim" },
  { id: 2, name: "Max" },
];
```

> Every element must match the `User` interface.

---

## 3. An array with several possible types (union)

```javascript
const data: (string | number)[] = [1, "two", 3, "four"];
```

> Every element must be either `string` or `number`.

---

## 4. An array of arrays (two-dimensional)

```javascript
const matrix: number[][] = [
  [1, 2],
  [3, 4],
];
```

> The type reads as "an array of arrays of numbers".

---

## 5. An immutable array (`readonly`)

If you need to forbid modifying the array:

```javascript
const ids: readonly number[] = [1, 2, 3];
ids.push(4); // Error: push is not allowed
```

or the equivalent form:

```javascript
const ids: ReadonlyArray<number> = [1, 2, 3];
```

> Useful for constant data (for example, lists of roles or statuses).

---

## 6. A fixed-length array (tuple)

> A tuple is a "fixed-length array" with element types known in advance.

```javascript
const pair: [string, number] = ["age", 25];
```

> `pair[0]` is always a string,
> `pair[1]` is always a number.

---

## 7. An array of unknown content (`any[]`)

```javascript
const arr: any[] = [1, "text", true, { key: "value" }];
```

> Such an array **disables type checking**,
> try to avoid `any[]` when you can specify an exact type.

---

## 8. An array with a generic

If a function needs to work with an array of any elements:

```javascript
function firstElement<T>(arr: T[]): T | undefined {
  return arr[0];
}

const n = firstElement([1, 2, 3]);       // n: number
const s = firstElement(["a", "b", "c"]); // s: string
```

> A universal way to write type-safe functions for arrays.

---

## 9. A type for an array via `type` or `interface`

```javascript
type StringArray = string[];
type Matrix = number[][];

interface UserArray {
  [index: number]: User;
}
```

> This lets you reuse the type in different places.

---

## Summary

| Task | Syntax | Example |
|---|---|---|
| Simple array of numbers | `number[]` | `[1, 2, 3]` |
| Array of strings | `string[]` | `["a", "b"]` |
| Alternative | `Array<number>` | `[1, 2, 3]` |
| Array of objects | `User[]` | `[{id:1,name:"Tim"}]` |
| Several types | `(string \| number)[]` | `["a", 1]` |
| Two-dimensional array | `number[][]` | `[[1,2],[3,4]]` |
| Read-only | `readonly string[]` | `["A","B"]` |
| Tuple | `[string, number]` | `["id", 5]` |

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