Arrays are used to store multiple values in a single variable.

Each value is called an element, and each element has a numeric position in the array, known as its index.

Arrays are zero-indexed, meaning the first element is at index 0, the second at index 1, and so on.

Arrays can contain any data type, including numbers, strings, and objects.

const arr1 = [2, 4, 6]; array

arr1[0]; element at index 0 → 2

arr1[1]; element at index 1 → 4

arr1[2]; element at index 2 → 6

arr1[3]; element at index 3 → undefined index not found

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Strings are a sequence of zero or more characters written inside quotes used to represent text.

Strings may consist of letters, numbers, symbols, words, or sentences.

Strings are immutable, they cannot be changed.

Each character in a string has an index.

The first character will be index 0 the second character will be index 1 and so on.

There are two ways to access an individual character in a string.

charAt() method

const str1 = "abc"; string

str1.charAt(0); character at index 0 → "a"

str1.charAt(1); character at index 1 → "b"

str1.charAt(2); character at index 2 → "c"

str1.charAt(3); character at index 3 → "" index not found

Alternatively use at() or slice() methods

bracket notation []

const str2 = "abc"; string

str2[0]; character at index 0 → "a"

str2[1]; character at index 1 → "b"

str2[2]; character at index 2 → "c"

str2[3]; character at index 3 → undefined index not found

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Numbers are used to represent both integer and floating-point values.

Numbers are most commonly expressed in literal forms like 255 or 3.14159 ↴

let num1 = 5; → number

let num2 = 2.5; → number

let num3 = num1 + num2;

console.log(num3); returns ↴

7.5 → number

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Find the difference between two arrays using ↴

Set Object → collection of unique values.

difference() method → takes a set and returns a new set containing elements in this set but not in the given set.

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Set Object is a collection of unique values.

Each value can only occur once, each value is unique.

const mySet = new Set();

console.log(mySet); returns ↴

Set(0) {size: 0} → empty Set

To add values to the Set we can use the add() method.

mySet.add("a");

mySet.add("b");

mySet.add("c");

console.log(mySet); returns ↴

Set(3) {"a", "b", "c"} → values added

Try to add a duplicate value.

mySet.add("c"); character "c" is already in mySet

console.log(mySet); returns ↴

Set(3) {"a", "b", "c"} → no change

To determine if mySet has an element present we can use the has() method.

mySet.has("a"); → true

mySet.has("d"); → false

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difference() method of Set instances takes a Set and returns a new Set containing elements in this Set but NOT in the given Set.

const arr2 = [1, 2, 3, 4];

const arr3 = [3, 4, 5, 6];

const setA = new Set(arr2); → this set

const setB = new Set(arr3); → given set

const setC = setA.difference(setB);

console.log(setC); returns ↴

Set(2) {1, 2} → set

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spread syntax ... unpacks the elements of an iterable object, like arrays and sets.

Convert an array to a Set.

const arr4 = [1, 2, 3, 4]; array

const setD = new Set(arr4);

console.log(setD); returns ↴

{1, 2, 3, 4} → set

Use spread syntax to convert a Set to an array.

const arr5 = [...setD];

console.log(arr5); returns ↴

[1, 2, 3, 4] → array

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Initialize the two input arrays to find their difference.

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Define a function findDifference() to find the difference of two arrays.

function findDifference(arr1, arr2) {}

The function takes two arrays as input arr1, arr2 and returns a new array with their difference. The original arrays remain unchanged.

Each input array may contain duplicates. Duplicates will be removed inside the function.

Set constructor is used to create two new Sets from from the input arrays arr1, arr2

setA = new Set(arr1) setA

setB = new Set(arr2) setB

Initialize a variable to hold the difference Set

const setDifference setDifference

difference() method takes a Set and returns a new Set containing elements in setA but NOT in setB

spread syntax ... converts the setDifference set to an array and returns it.

return [...setDifference] → array

The function returns a new array containing elements that are present in the first array but not in the second array.

If there is no difference between the two arrays then an empty array is returned.

Alternatively ↴

difference() method takes a Set and returns a new Set containing elements in setB but NOT in setA

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Find elements in first array that are NOT in the second array.

Create a Set from the first array to store unique values.

const setA = new Set(arr1);

Create a Set from the second array to store unique values.

const setB = new Set(arr2);

Calculate the difference of both sets.

Return the difference Set as an array.

return [...setDifference];

Alternatively ↴

Find elements in second array that are NOT in the first array.

Calculate the difference of both sets.

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Call the function with ↴

findDifference(array1, array2);

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Find elements in first array that are NOT in the second array.

Find the difference of two arrays.

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Find elements in second array that are NOT in the first array.

Find the difference of two arrays.

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Alternative to convert a Set to an Array ↴

const mySet = new Set([1, 2, 3, 4]);

const myArray = Array.from(mySet);

console.log(myArray); returns ↴

[1, 2, 3, 4] → array

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Alternative - return directly without using a variable ↴