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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Capitalize the first letter of each word in an array using ↴

map() method → creates a new array from calling a function for every array element.

charAt() method → returns the character at a specified index in a string.

slice() method → extracts a part of a string and returns it as a new string, without modifying the original string.

toLowerCase() method → returns the value of the string converted to lower case.

toUpperCase() method → returns the value of the string converted to upper case.

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map() method creates a new array populated with the results of calling a provided function on every element in the calling array. The original array is unchanged.

const arr2 = [5, 10, 15, 20];

arr2.map((x) => x + 10); returns ↴

[15, 20, 25, 30] → 10 added to each element

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charAt() method returns the character at the given index.

If the index is out of range an empty string "" is returned.

const str3 = "hello";

str3.charAt(0); → "h" first character

str3.charAt(1); → "e"

str3.charAt(2); → "l"

str3.charAt(3); → "l"

str3.charAt(4); → "o"

str3.charAt(5); → "" not found

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slice() method extracts a part of a string and returns it as a new string, without modifying the original string.

syntax ↴

slice(start) return a new string from start index to end of string

slice(start, end) return a string from start index to end index of string (exclusive).

Return a new string from index 1 to end of string.

const str4 = "Hello World";

str4.slice(1); start index is 1

returns ↴

"ello World"

Return a new string from index 1 to index 9 (exclusive).

const str5 = "Hello World";

str5.slice(1, 9); start index is 1 end index is 9 (not included)

returns ↴

"ello Wor"

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toLowerCase() method returns a new string with all letters converted to lower case. The original string is unchanged.

const str6 = "hELlo wORLd";

str6.toLowerCase(); returns ↴

"hello world" → lower case

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toUpperCase() method returns a new string with all letters converted to upper case. The original string is unchanged.

const str7 = "hELlo wORLd";

str7.toUpperCase(); returns ↴

"HELLO WORLD" → uppercase

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Initialize a variable to hold the array to capitalize the first letter of each word in an array.

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Define a function capArrWords to capitalize the first letter of each word in an array.

function capArrWords(arr) {}

The function takes an array as input arr and returns a new array with the first letter of each word capitalized and the rest of the word converted to lower case. The original array is unchanged.

map() method creates a new array by applying a callback function to each element of the array.

map(calbackFn) ↴

callback function ↴

(word) => word.charAt(0).toUpperCase() + word.slice(1).toLowerCase()

For each word in the array, capitalize first letter and lower case rest of the word.

Return the array.

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Call the function with ↴

capArrWords(array1);

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Capitalize the first letter of each word in an array.