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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Count number of words in a string using ↴

matchAll method → returns an iterator of results after matching a string against a regular expression.

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

Array.from() method → creates a new array instance from an array-like or iterable object.

length property → set or return the number of elements in an array.

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Array.from() method returns an array from any object with a length property, such as arrays, strings, sets, etc.

const str3 = "Hello"; string

Array.from(str3); returns ↴

["H", "e", "l", "l", "o"] → array

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

The Regular Expression /\b\w+\b/g finds all words in the string.

\b denotes a word boundary, ensuring that we only match whole words.

\w+ matches one or more word characters (letters, digits, or underscores).

g flag indicates a global search, allowing the function to find all matches in the string.

match(/\b\w+\b/g) will split the string into an array of words.

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matchAll() method returns an Iterator of results after matching a string against a regular expression.

Iterator → object that provides a standard way to access elements sequentially.

Find all capital letters in the string.

['H', index: 0, input: 'Hello World', groups: undefined] → array

['W', index: 6, input: 'Hello World', groups: undefined] → array

arr2[0][0]; returns ↴

"H" → first element in first array

arr2[1][0]; returns ↴

"W" → first element in second array

The global flag g must be set, otherwise a TypeError is thrown.

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length property returns the number of elements in an array.

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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

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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.

The regular expression \b\w+\b matches sequences of word characters that are bounded by word boundaries.

Use matchAll to find all words in the string.

str.matchAll(/\b\w+\b/g)

Array.from() converts the iterator returned by matchAll into an array.

Array.from(str.matchAll(/\b\w+\b/g)) → array

Return the length of the array, which is the word count.

.length

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Call the function with ↴

countWords(string1);

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Count number of words in a string.

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Alternative ↴

Instead of Array.from method use the spread syntax