Interesting Facts about JavaScript Arrays

Last Updated : 10 Nov, 2024

Let us talk about some interesting facts about JavaScript Arrays that can make you an efficient programmer.

Arrays are Objects

JavaScript arrays are actually specialized objects, with indexed keys and special properties. They have a length property and are technically instances of the Array constructor.

JavaScript

const a = [10, 20, 30]; console.log(typeof a);

Output

object

You can add non-integer properties to arrays, making them work partly like objects. However, this is usually discouraged for clarity.

JavaScript

let a = [1, 2, 3];  // Adding a property to array (NOT RECOMMEMDED IN PRACTICE) a.name = "MyArray";  console.log(a.name);         // Iterating through the array with `for...in` // (NOT RECOMMENDED IN PRACTICE) for (let key in a) {   console.log(`${key}: ${a[key]}`); }

Output

MyArray 0: 1 1: 2 2: 3 name: MyArray

Mixed Elements Allowed

Like Python and unlike C/C++/Java,, we can have mixed type of elements in a JavaScript array.

JavaScript

const a = [10, "hi", true]; console.log(a);

Output

[ 10, 'hi', true ]

Dynamic Size

Like Python and unlike C/C++/Java,, the default array implementation is Dynamic Size.

JavaScript

let a = [1, 2, 3]; a.push(4); console.log(a);

Output

[ 1, 2, 3, 4 ]

Negative Indexing

The .at() method, introduced in ES2022, allows access to array elements using negative indices, making it easy to retrieve elements from the end of an array without calculating the length.

JavaScript

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

Output

Resizing an Array

We can resize a JavaScript array by simply changing its length property.

JavaScript

let a = [1, 2, 3, 4]; a.length = 2; console.log(a);

Output

[ 1, 2 ]

Array Assignment

When we assign an array to another, it only creates one more reference to the same array.

JavaScript

// changed the original array let a = [10, 20]; let b = a; b.push(30); console.log(a);

Output

[ 10, 20, 30 ]

Spread Operator

We get members of an array or a string. It helps us in copying in copying an array, concatenating arrays and passing array elements to different parameters of a function.

JavaScript

// Arrat copy using spread operator let a = [10, 20]; let b = [...a]; b.push(30); console.log(a);

Output

[ 10, 20 ]

JavaScript

// Array concatenation using spread operator let a = [10, 20]; let b = [30, 40]; let c = [...a, ...b] console.log(c);

Output

[ 10, 20, 30, 40 ]

JavaScript

function add(x, y, z) { return x + y + z; } let a = [10, 20, 30]; console.log(add(...a));

Output

Empty Elements in Array

JavaScript allows empty elements in an array. When we access these elements, we get undefined.

JavaScript

const a = [1, , , 3]; console.log(a); console.log(a[1]);

Output

[ 1, <2 empty items>, 3 ] undefined

JavaScript

const a = [1, 3]; a.length = 4 console.log(a); console.log(a[2]);

Output

[ 1, 3, <2 empty items> ] undefined

Direct Methods to Modify Arrays

JavaScript allows multiple direct methods for efficient programming.

JavaScript

const a = [1, 2, 3, 4];  const b = a.map(x => x * 2);  console.log(b)  const c = a.filter(x => x > 2);  console.log(c)  const d = [1, [2, 3], [4, [5]]]; console.log(d.flat(2));

Output

[ 2, 4, 6, 8 ] [ 3, 4 ] [ 1, 2, 3, 4, 5 ]

Interesting Facts about Object in JavaScript

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Interesting Facts about JavaScript Arrays

Arrays are Objects

Mixed Elements Allowed

Dynamic Size

Negative Indexing

Resizing an Array

Array Assignment

Spread Operator

Empty Elements in Array

Direct Methods to Modify Arrays

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