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

---

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

---

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

---

Convert string to snake 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.

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

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

Regular Expression → patterns used to match character combinations in strings.

ternary operator → frequently used as an alternative to an if...else statement.

---

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

---

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

const str4 = "hELlo wORLd";

str4.toLowerCase(); returns ↴

"hello world" → lower case

---

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

const str5 = "Hello"; → string

str5.split(""); returns ↴

["H", "e", "l", "l", "o"] → array

const str6 = "hello world"; → string

str6.split(" "); returns ↴

["hello", "world"] → array

---

Regular expressions are patterns used to match character combinations in strings.

The Regular Expression /\s+/ matches one or more whitespace characters.

\s matches any whitespace character (spaces, tabs, line breaks).

+ quantifier indicates that one or more occurrences of the preceding element (whitespace in this case) should be matched.

As a result, this regex will match any sequence of whitespace characters, effectively splitting the string at each space.

This means that multiple spaces between words will not create empty entries in the resulting array.

---

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)

---

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

---

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

---

Ternary Operator

Ternary Operator is frequently used as an alternative to if...else statements.

if (condition) {

expressionIfTrue;

} else {

expressionIfFalse;

}

Ternary Operator takes three operands ↴

condition evaluates to true or false.

? question mark → expression to execute if the condition is truthy

: colon → expression to execute if the condition is falsy

condition ? expressionIfTrue : expressionIfFalse

let score = 75;

let result = score >= 55

? "You passed"

: "You failed";

console.log(result); returns ↴

You passed → first expression executed

---

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

---

Define a function toSnakeCase to transform a string into snake case.

function toSnakeCase(str) {}

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

Trim whitespace from both ends of the string str

str.trim()

Convert the string to lower case.

.toLowerCase()

The regular expression /\s+/ matches one or more whitespace characters, effectively handling multiple spaces between words.

This means that multiple spaces between words will not create empty strings in the array.

Split the string into an array of words using one or more spaces as the delimiter.

.split(/\s+/) → returns an array

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

reduce() method iterates over the array of words and concatenates them into a single string, inserting an underscore between words.

snakeWord accumulated snake case string.

Using a ternary operator, the condition (snakeWord ? "_" : "") ensures that an underscore is only added if there is already a word in the accumulator and is not empty.

currWord current element.

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

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

---

Call the function with ↴

toSnakeCase(string1);

---

Convert string to snake case.