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 union of two arrays using ↴

Set Object → collection of unique values.

union() method → takes a set and returns a new set containing elements which are in either or both of this set and 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.

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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union() method of Set instances takes a set and returns a new set containing all elements in this set and 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.union(setB);

console.log(setC); returns ↴

Set(2) {1, 2, 3, 4, 5, 6} → 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 union.

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Define a function findUnion() to find the union of two arrays.

function findUnion(arr1, arr2) {}

The function takes two arrays as input arr1, arr2 and returns a new array with their union. 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 union Set

const setUnion setUnion

union() method takes a Set and returns a new Set containing unique elements in both setA and setB

setUnion = setA.union(setB)

spread syntax ... converts the setUnion Set to an Array and returns it.

return [...setUnion] → array

The array is returned with all the unique elements that are present in both arrays.

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

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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 union of both sets.

const setUnion = setA.union(setB);

Return the union set as an array.

return [...setUnion];

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Call the function with ↴

findUnion(array1, array2);

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Find the union of two arrays.

const array1 = [1, 2, 3, 4, 5];

const array2 = [4, 5, 6, 7, 8];

function findUnion(arr1, arr2) {

const setA = new Set(arr1);

const setB = new Set(arr2);

const setUnion = setA.union(setB);

return [...setUnion];

}

call function

findUnion(array1, array2); returns ↴

[1, 2, 3, 4, 5, 6, 7, 8]

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Alternative to convert a Set to an Array ↴

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

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 ↴

const setUnion = setA.union(setB);

return [...setUnion]; ↴

return [...setA.union(setB)];