const numbers = [1, 2, 3, 4, 5];

const numbers1 = new Array(1, 2, 3, 4, 5);

const names = Array.of("Alice", "Bob", "Charlie");

const numbers: number[] = [1, 2, 3, 4, 5];

const numbers1: number[] = new Array(1, 2, 3, 4, 5);

const names: string[] = Array.of("Alice", "Bob", "Charlie");

=====================

ARRAYS IN TYPESCRIPT

=====================

=====================

1. INTRODUCTION

=====================

An array in TypeScript is a data structure that stores multiple values of the same type in a single variable.

Syntax:

-------

let arr: type[] = [val1, val2, val3];

OR

let arr: Array<type> = [val1, val2, val3];

=====================

2. DECLARING ARRAYS

=====================

Method 1 – Using square brackets:

----------------------------------

let numbers: number[] = [1, 2, 3, 4];

Method 2 – Using generic Array type:

------------------------------------

let names: Array<string> = ["Ali", "Waseem", "Sara"];

Both are valid and work the same.

========================

3. COMMON ARRAY TYPES

========================

- number[] – array of numbers

- string[] – array of strings

- boolean[] – array of booleans

- any[] – array with mixed types (not recommended for strict typing)

Example:

--------

let mixed: any[] = [1, "hello", true];

==============================

4. ARRAY METHODS (BUILT-IN)

==============================

- push() → Adds item to end

- pop() → Removes last item

- shift() → Removes first item

- unshift() → Adds item to start

- concat() → Merges arrays

- slice() → Returns a portion

- splice() → Adds/removes elements

- indexOf() → Finds index

- includes() → Checks existence

- map(), filter(), reduce() → Iterates and transforms data

Example:

--------

let arr: number[] = [10, 20, 30];

arr.push(40); // [10, 20, 30, 40]

arr.pop(); // [10, 20, 30]

let doubled = arr.map(x => x * 2); // [20, 40, 60]

===============================

5. LOOPING OVER ARRAYS

===============================

Using for loop:

---------------

for (let i = 0; i < arr.length; i++) {

console.log(arr[i]);

}

Using for...of:

---------------

for (let val of arr) {

console.log(val);

}

Using forEach:

--------------

arr.forEach(item => console.log(item));

===============================

6. ARRAY OF OBJECTS

===============================

let users: { id: number, name: string }[] = [

{ id: 1, name: "Waseem" },

{ id: 2, name: "Ali" }

];

console.log(users[0].name); // Output: Waseem

===============================

7. MULTI-DIMENSIONAL ARRAYS

===============================

let matrix: number[][] = [

[1, 2],

[3, 4],

[5, 6]

];

console.log(matrix[1][0]); // Output: 3

===============================

8. TYPING WITH INTERFACES

===============================

interface Product {

id: number;

name: string;

}

let products: Product[] = [

{ id: 101, name: "Pen" },

{ id: 102, name: "Book" }

];

===============================

9. INTERVIEW PRO TIPS

===============================

✅ Q: What is the difference between `any[]` and `unknown[]`?

A: `any[]` allows any operations without checks. `unknown[]` requires type-checking before use.

✅ Q: How do you ensure type safety in arrays?

A: Use typed arrays like `string[]`, `number[]`, or use interfaces.

✅ Q: Can an array hold multiple types?

A: Yes, using union types or `any[]`.

Example: let mixed: (number | string)[] = [1, "two", 3];

✅ Q: What’s the difference between `Array<number>` and `number[]`?

A: Both are the same in behavior; just different syntax.

✅ Q: Can you use readonly arrays?

A: Yes. Use `readonly number[]` to make it immutable.

===============================

10. BEST PRACTICES

===============================

- Prefer specific types (`string[]` or `User[]`) over `any[]`.

- Use interfaces for array of objects.

- Use array methods like `map`, `filter`, and `reduce` for clean and functional code.

- Use `readonly` modifier for immutable arrays:

const nums: readonly number[] = [1, 2, 3];

===============================

11. CONCLUSION

===============================

Arrays in TypeScript are powerful and flexible. They allow strong typing while still being easy to use and manipulate.

Understanding how to declare, type, and use arrays effectively is crucial for both real-world coding and technical interviews.

===============================

END OF NOTES

===============================

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