Arrays in JS

What is an Array?

An Array is an object type designed for storing data collections.

Key characteristics of JavaScript arrays are:

Elements: An array is a list of values, known as elements.

Ordered: Array elements are ordered based on their index.

Zero indexed: The first element is at index 0, the second at index 1, and so on.

Dynamic size: Arrays can grow or shrink as elements are added or removed.

Heterogeneous: Arrays can store elements of different data types (numbers, strings, objects and other arrays).

Declaring an Array
1. Array Literal (Most Used)

let arr = [1, 2, 3, 4];

2. Using Constructor

let arr = new Array(1, 2, 3);

Accessing Elements

let arr = [10, 20, 30];

console.log(arr[0]); // 10
console.log(arr[1]); // 20

Use index number to access

Basic Array Methods
1. length
Returns number of elements

let arr = [1, 2, 3];
console.log(arr.length); // 3

2. toString()
Converts array to string

let arr = [1, 2, 3];
console.log(arr.toString()); // "1,2,3"

3. at()(To be discussed)
Access element using index (supports negative index)

let arr = [10, 20, 30];
console.log(arr.at(-1)); // 30

4. join()
Joins elements with separator

let arr = [1, 2, 3];
console.log(arr.join("-")); // "1-2-3"

5. pop()
Removes last element

let arr = [1, 2, 3];
arr.pop();
console.log(arr); // [1,2]

6. push()
Adds element at end

arr.push(4);

7. shift()
Removes first element

arr.shift();

8. unshift()
Adds element at beginning

arr.unshift(0);

9. Array.isArray()
Checks if variable is array

Array.isArray(arr); // true

10. delete
Removes element but leaves empty slot ⚠️

let arr = [1, 2, 3];
delete arr[1];

console.log(arr); // [1, empty, 3]

❌ Not recommended

11. concat()
Merges arrays

let a = [1, 2];
let b = [3, 4];

let c = a.concat(b);
console.log(c); // [1,2,3,4]

12. copyWithin()
Copies part of array to another position

let arr = [1, 2, 3, 4];
arr.copyWithin(0, 2);

console.log(arr); // [3,4,3,4]

13. flat()
Flattens nested arrays

let arr = [1, [2, 3]];
console.log(arr.flat()); // [1,2,3]

14. slice()
Extracts part of array (no change to original)

let arr = [1, 2, 3, 4];
let result = arr.slice(1, 3);

console.log(result); // [2,3]

15. splice()
Adds/removes elements (modifies original)

let arr = [1, 2, 3];
arr.splice(1, 1);

console.log(arr); // [1,3]

Add elements:

arr.splice(1, 0, 5);

16. toSpliced()
Same as splice but does NOT modify original

let arr = [1, 2, 3];

let newArr = arr.toSpliced(1, 1);

console.log(newArr); // [1,3]
console.log(arr);    // [1,2,3]