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 camel case using ↴

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

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

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

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

slice() method → returns selected elements in an array, as a new array.

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

const str3 = " Hello World "; → string with leading and trailing whitespace

str3.trim(); returns ↴

"Hello World" → string without whitespace

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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 str4 = "Hello"; → string

str4.split(""); returns ↴

["H", "e", "l", "l", "o"] → array

const str5 = "hello world"; → string

str5.split(" "); returns ↴

["hello", "world"] → array

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

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

const str6 = "hello";

str6.charAt(0); → "h" first character

str6.charAt(1); → "e"

str6.charAt(2); → "l"

str6.charAt(3); → "l"

str6.charAt(4); → "o"

str6.charAt(5); → "" not found

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slice() method returns selected elements in an array, as a new array. The original array is unchanged.

syntax ↴

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

slice(start, end) return an array from start index to end index of array (exclusive).

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

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

arr4.slice(1); start index is 1

returns ↴

[2, 3, 4]

Return a new array from index 1 to index 4 (exclusive).

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

arr5.slice(1, 3); start index is 1 end index is 4 (not included)

returns ↴

[2, 3]

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toLowerCase() method converts all letters to lower case. The original string is unchanged.

const str7 = "hELlo wORLd";

str7.toLowerCase(); returns ↴

"hello world" → lower case

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toUpperCase() method converts all letters to upper case. The original string is unchanged.

const str8 = "hELlo wORLd";

str8.toUpperCase(); returns ↴

"HELLO WORLD" → upper case

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To capitalize a word

Convert entire string to lower case.

Capitalize first character.

Concatenate with the rest of the string.

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Initialize a variable to hold the string to transform to camel case.

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Define a function toCamelCase to transform a string into camel case.

function toCamelCase(str) {}

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

Trim whitespace from both ends of the string str

str.trim()

Convert the string to lower case.

.toLowerCase()

Split the string into an array of words.

.split(" ") → returns an array

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

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

reduce(callbackFn, initialValue) ↴

reduce((camelWord, currWord) => ())

callback function ↴

(camelWord, currWord) =>

camelWord + (currWord.charAt(0).toUpperCase() + currWord.slice(1))

initial value ↴

"" empty string

For each word, capitalize the first letter and concatenate it to the result.

reduce() methods optional initial value is not used, so it will be initialized to the first value in the array.

This prevents the first character of the first word from being capitalized.

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

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

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Call the function with ↴

toCamelCase(string1);

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Convert string to camel case.