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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Remove duplicates from an array using ↴

forEach() method → calls a function for each element in an array, executing a provided function once for each array element.

includes() method → returns true if an array contains a specified value, otherwise returns false.

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

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forEach() method calls a function for each element in an array, executing a provided function once for each array element.

The method does not return a new array, it always returns undefined

const arr2 = [2, 4, 6, 8];

arr2.forEach((element, index, array) => {

array[index] = element * 2;

});

console.log(arr2); returns ↴

[4, 8, 12, 16] → value of each element is doubled

const arr3 = [2, 4, 6, 8];

arr3.forEach((element, index) => {

console.log(index, element)

}); returns ↴

0 2

1 4

2 6

3 8 → index and element printed to console

Use forEach() when an action is needed to be performed on each element,

not when a new array needs to be generated from the current one.

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includes() method determines whether an array includes a certain value among its entries, returning true or false

const arr4 = [1, 2, 3, 4, 5, 6];

arr4.includes(4); returns boolean ↴

true → 4 found in array

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

arr5.includes(7); returns boolean ↴

false → 7 NOT found in array

logical NOT ! syntax converts a true value to a false and vice-versa.

!arr4.includes(7); returns boolean ↴

true → 7 NOT found in array

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

Add 4 to end of array.

const arr6 = [1, 2, 3];

arr6.push(4);

console.log(arr6); returns ↴

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

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

arr6 is modified.

Using the spread operator creates a new array.

Add 4 to a new array.

const arr7 = [1, 2 , 3];

const arr8 = [...arr7, 4];

console.log(arr8); returns ↴

[1, 2, 3, 4] → 4 added to new array

console.log(arr7); returns ↴

[1, 2 ,3]

arr7 remains unchanged.

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Initialize an array from which to remove duplicates

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Define a function removeDuplicates to return a new array with all duplicates removed.

function removeDuplicates(arr) {}

The function takes an array as input arr and returns a new array with all duplicate values removed.

Initialize an empty array to hold unique values.

const uniqueArr = [] uniqueArr

forEach() method loops through the array, executing a callback function once for each array element.

arr.forEach(callbackFn) ↴

callback function ↴

(element) => {

if (!uniqueArr.includes(element)) {

uniqueArr.push(element)

}

}

element → current element being processed in the array.

Check if element is NOT already in uniqueArr

if (!uniqueArr.includes(element)) {}

If true, it is NOT already in uniqueArr, then add it to uniqueArr

uniqueArr.push(element)

Return the array with duplicates removed.

return uniqueArr

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Call the function with ↴

removeDuplicates(array1);

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Remove duplicates from array.

arr = [1, 2, 1, 2, 4, 3, 2, 1];

uniqueArr = [];

!uniqueArr.includes(element)

If element NOT found in uniqueArr, add it to the array.

push(x) where x is the current element.

If element found in the in the array, ignore it.

Initial value:

uniqueArr [] Initial value: empty array

returns ↴

[1, 2, 4, 3] No duplicate values. All values are unique.

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Remove duplicates from array.

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

function removeDuplicates(arr) {

let uniqueArr = [];

arr.forEach((element) => {

if (!uniqueArr.includes(element)) {

uniqueArr.push(element);

}

});

return uniqueArr;

};

call function

removeDuplicates(array1); returns ↴

[1, 2, 4, 3]