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 ↴

for loop → executes a block of code a number of times.

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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for loop repeatedly executes a block of code until a specified condition evaluates to false.

The loop runs a block of code a set number of times, defined by an initialization, a condition, and an increment.

const arr = []; → empty array

for (let x = 0; x < 4; x++) {

arr.push(x);

}

console.log(arr);

Initialize an empty array arr

Loop variable x is initialized to 0

Condition x < 4 is checked before each iteration.

The loop will continue to run as long as x is less than 4

The loop repeatedly executes a block of code 4 times, from 0 to 3

For each iteration of the loop, the current value of x is pushed to the end of the array.

After each iteration, x is incremented by 1 x++

When x reaches 4 the condition evaluates to false, terminating the loop.

[0, 1, 2, 3] → array returned

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

const arr2 = [1, 2, 3, 4, 5, 6];

arr2.includes(4); returns boolean ↴

true → 4 found in array

const arr3 = [1, 2, 3, 4, 5, 6];

arr3.includes(7); returns boolean ↴

false → 7 NOT found in array

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

!arr3.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 arr4 = [1, 2, 3];

arr4.push(4);

console.log(arr4); returns ↴

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

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

arr4 is modified.

Using the spread operator creates a new array.

Add 4 to a new array.

const arr5 = [1, 2 , 3];

const arr6 = [...arr5, 4];

console.log(arr6); returns ↴

[1, 2, 3, 4] → 4 added to new array

console.log(arr5); returns ↴

[1, 2 ,3]

arr5 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

Loop through each element in arr

for (let x = 0; x < arr.length; x++) {}

Check if the current element arr[x] is not already in uniqueArr

if (!uniqueArr.includes(arr[x])) {}

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

uniqueArr.push(arr[x])

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(arr[x])

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

push(x)

If it already exists in the array, ignore it.

uniqueArr [] Inital 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) {

const uniqueArr = [];

for (let x = 0; x < arr.length; x++) {

if (!uniqueArr.includes(arr[x])) {

uniqueArr.push(arr[x]);

}

}

return uniqueArr;

}

call function

removeDuplicates(array1); returns ↴

[1, 2, 4, 3]