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 ↴

concat() method → merge two or more arrays.

filter() method → creates a new array filled with elements that pass a test provided by a function.

indexOf() method → returns the first index at which a given element can be found in an array.

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concat() method is used to merge two or more arrays.

This method does not change the existing arrays, but instead returns a new array.

const arr2 = [1, 2, 3, 4, 5];

const arr3 = [4, 5, 6, 7, 8];

const arr4 = arr2.concat(arr3);

console.log(arr4); returns ↴

[1, 2, 3, 4, 5, 4, 5, 6, 7, 8] → values are not unique

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filter() method iterates over each element of an array.

It creates and returns a new array containing only the elements that pass a test provided by a function.

Return a new array with values greater than 4

const arr5 = [1, 2, 3, 4, 5, 6, 7, 8, 9];

arr5.filter((num) => num > 4); returns ↴

[5, 6, 7, 8, 9] → numbers greater than 4

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indexOf() method returns the first index at which a given element can be found in an array, or -1 if it is not present.

Find first index of element 6 in the array.

const arr6 = [2, 4, 6, 8, 6, 4];

arr6.indexOf(6); returns ↴

2 → index of first occurrence of element 6

Element is present.

Find first index of element 9 in the array.

const arr7 = [2, 4, 6, 8, 6, 4];

arr7.indexOf(9); returns ↴

-1 → element 9 NOT found in array.

Element NOT present.

array.indexOf(element) !== -1

If result is NOT -1 then the element is present in the 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.

concat() method merges the two input arrays arr1, arr2, into a new array.

arr1.concat(arr2)

filter() method iterates over each element of the concatenated array.

filter(calbackFn) ↴

It creates a new array filtered with elements that pass a test provided by a callback function.

indexOf() method checks each element's index against the first occurrence of that element in the array.

arr.indexOf(value) === index

If the index matches, the element is unique and is included in the new array, effectively removing duplicates.

The function returns a new array containing 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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Concatenate arr1, arr2 into a single array.

let union = arr1.concat(arr2)

Filter out duplicate values using indexOf() method.

Return the resulting array containing the union.

return union

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Call the function with ↴

findUnion(array1, array2);

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Find union of two arrays.

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Alternative ↴

Instead of concat() method use the spread syntax to merge arrays.

arr1.concat(arr2) ↴

[...arr1, ...arr2]