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

---

Count number of words in a string using ↴

for...of loop → iterates through the values of an iterable object, such as an Array, String, Set, Map, ...

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

test() method of RegExp instances → tests for a match in a string. If it finds a match, it returns true, otherwise it returns false.

---

for...of loop iterates through the values of an iterable object, such as an Array, String, Set, Map, ...

syntax

for (variable of iterable) {}

variable holds the current value of the iteration.

of keyword indicates that the loop should iterate over the values of the iterable.

iterable object that is iterable, such as an Array, String, Set, Map, ...

Iterate over each character in the string.

const str3 = "ABC";

for (const char of str3) {

console.log(char);

} returns ↴

A

B

C → printed to console

The loop will run three times, once for each character in the string.

On each iteration, the value of the current element is stored in the variable char

For each iteration of the loop, the current value of char is printed to the console.

---

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.

---

test() method of RegExp instances tests for a match in a string. If it finds a match, it returns true, otherwise it returns false.

const str6 = "Hello World";

Test pattern Hello for a match in the string.

const pattern1 = /Hello/g;

pattern1.test(str6); returns ↴

true

Test pattern Bye for a match in the string.

const pattern2 = /Bye/g;

pattern2.test(str6); returns ↴

false

---

Initialize a variable to hold the string to count number of words.

const string1 = "The quick brown fox jumps over the lazy dog"; → user input

---

Define a function countWords to count number of words in a string.

function countWords(str) {}

The function takes a string as input, str and returns the number of words found in that string.

Initialize word count.

let count = 0 count

Boolean flag to track if we are inside a word.

let inWord = false inWord

Iterate through each character in the string.

for (const char of str)

Check if the character is a whitespace.

if (/\s/.test(char))

If true, set inWord to false if whitespace is found.

inWord = false

else if not a whitespace, it must be a character.

else if (!inWord)

If true, set inWord to true if a new word is found.

inWord = true

Increment the word count by 1

count++

Return the total word count.

return count

---

Call the function with ↴

countWords(string1);

---

Count number of words in a string.