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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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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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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Convert string to title case using ↴

reduce() method → executes a reducer function, resulting in a single output value.

split() method → splits a string into an array of substrings.

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.

trim() method → removes whitespace from both ends of the string and returns a new string, without modifying the original string.

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reduce() method iterates over each element in an array, and each iteration returns a single value, which is the accumulator.

When the iteration is finished, the accumulator value will be returned from the method.

It takes two parameters: a callback function and an optional initial value ↴

callback function first parameter.

initialValue second parameter. The accumulator is initialized to the first element of the array if no initial value is provided.

The callback function takes four parameters ↴

accumulator The value resulting from the previous call to callback function - required.

currentValue The value of the current element - required.

currentIndex Index position of currentValue in the array - optional.

Array The array reduce() was called upon - optional.

syntax

array.reduce(callback, initialValue); ↴

array.reduce((accumulator, currentValue, currentIndex, Array), initialValue)

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Example 1 | Find the sum of the array ↴

During each iteration, the current value cur will be added to the accumulator acc ↴

acc + cur

Iteration ↴

0 acc Initial value → 0

1 acc 0 → 0 + 1 = 1 → 1

2 acc 1 → 1 + 2 = 3 → 3

3 acc 3 → 3 + 3 = 6 → 6

4 acc 6 → 6 + 4 = 10 → 10

5 acc 10 → 10 + 5 = 15 → 15

6 acc 15 → 15 + 6 = 21 → 21

The return value becomes the value of the accumulator parameter acc on the next invocation of the callback function.

For the last invocation, the return value becomes the return value of reduce()

When the iteration is finished, the accumulator value will be returned ↴

21 → sum of the array

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Example 2 | Find even numbers ↴

During each iteration, the ternary operator evaluates the condition cur % 2 === 0

If current element cur is divisible by 2, it will be added to the accumulator array, acc

[...acc, cur] ↴

cur % 2 === 0 ? [...acc, cur] : acc

If current element cur not divisible by 2, the accumulator acc will be returned as is.

The return value becomes the value of the accumulator parameter acc on the next invocation of the callback function.

For the last invocation, the return value becomes the return value of reduce()

When the iteration is finished, the accumulator value will be returned ↴

[12, 14, 16] → even numbers

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split() method splits a string into an array of substrings based on a specified separator (delimiter). The original string is unchanged.

const str3 = "Hello"; → string

str3.split(""); returns ↴

["H", "e", "l", "l", "o"] → array

const str4 = "hello world"; → string

str4.split(" "); returns ↴

["hello", "world"] → array

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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 str5 = "hello";

str5.charAt(0); → "h" first character

str5.charAt(1); → "e"

str5.charAt(2); → "l"

str5.charAt(3); → "l"

str5.charAt(4); → "o"

str5.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 str6 = "Hello World";

str6.slice(1); start index is 1

returns ↴

"ello World"

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

const str7 = "Hello World";

str7.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 str8 = "hELlo wORLd";

str8.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 str9 = "hELlo wORLd";

str9.toUpperCase(); returns ↴

"HELLO WORLD" → uppercase

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trim() method removes whitespace from both ends of a string and returns a new string, without modifying the original string.

const str10 = " Hello World "; → string with leading and trailing whitespace

str10.trim(); returns ↴

"Hello World" → string without whitespace

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Initialize a variable to hold the string to tranform to title case.

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Define a function toTitleCase to tranform a string into title case.

function toTitleCase(str) {}

The function takes a string as input str and returns a new string that is transformed into title case. The original string remains unchanged.

Convert the string str to lower case.

return str.toLowerCase()

Split the string into an array of words based on spaces.

split(" ")

Use reduce() method to convert array of words to title case.

reduce() method iterates over the array of words and concatenates them into a single string, capitalizing the first letter of each word, adding a space character, and appending the rest of the word.

The return value becomes the value of the accumulator parameter titleWord on the next invocation of the callback function.

For the last invocation, the return value becomes the return value of reduce()

Trim any leading or trailing whitespaces.

.trim()

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Call the function with ↴

toTitleCase(string1);

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Convert string to title case.

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Alternatives to split the string by one or more spaces to eliminate multiple spaces within the string

.split(" ") ↴

.split(/\s+/)