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.

push() method → adds specified elements to the end of an array and returns the new length of the array.

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

All the elements of a second array can be pushed into the first array using the spread syntax.

The first array will be modified.

const arr3 = [1, 2, 3, 4, 5];

const arr4 = [4, 5, 6, 7, 8];

arr3.push(...arr4);

console.log(arr3); returns ↴

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

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push() method adds new elements to the end of an array.

Add 4 to end of array.

const arr5 = [1, 2, 3];

arr5.push(4);

console.log(arr5); returns ↴

[1, 2, 3, 4] → 4 added to end of array

The push() method changes the length of the array.

arr5 is modified.

Using the spread operator creates a new array.

Add 4 to a new array.

const arr6 = [1, 2 , 3];

const arr7 = [...arr6, 4];

console.log(arr7); returns ↴

[1, 2, 3, 4] → 4 added to new array

console.log(arr6); returns ↴

[1, 2 ,3]

arr6 remains unchanged.

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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. Array arr1 is modified.

Each input array may contain duplicate elements. The function will eliminate any duplicates.

spread syntax ... takes all the elements from the second array arr2

and spreads them out as individual arguments to the push() method.

push() method adds the elements of arr2 to the first array arr1

arr1.push(...arr2) → array arr1 is modified.

Set constructor creates a new Set from arr1, which automatically removes any duplicate values.

new Set(arr1) creates a new Set from elements of the modified arr1

The spread syntax converts the Set back into an array.

const union = [...new Set(arr1)] union

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

return union

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

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Use the spread syntax to append elements of arr2 to arr1

arr1.push(...arr2)

Create a new Set from the modified arr1 to remove duplicates and convert it back to an array.

const union = [...new Set(arr1)]

Return the array containing unique elements.

return union

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Call the function with ↴

findUnion(array1, array2);

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Find union of two arrays.

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

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

function findUnion(arr1, arr2) {

arr1.push(...arr2);

const union = [...new Set(arr1)];

return union;

}

call function

findUnion(array1, array2); returns ↴

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

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Alternative ↴

Instead of the push() method use the spread syntax ... to append elements of arr2 to arr1. Array arr1 remains unchaned.

arr1.push(...arr2); → arr1 updated

const arr3 = [...arr1, ...arr2]; → arr1 unchanged

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Alternative using spread syntax ... ↴

Return unique values from union of two arrays.

const arr4 = [1, 2, 3, 4, 5];

const arr5 = [4, 5, 6, 7, 8];

[...new Set([...arr4, ...arr5])]; returns ↴

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

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Alternative using Array.from ↴

Return unique values from union of two arrays.