JavaScript - How to Get a Number of Vowels in a String?

Here are the various methods to get the number of vowels in a string using JavaScript.

1. Using a for Loop

This is the most basic and beginner-friendly approach. It uses a loop to iterate over each character and checks if it is a vowel.

const cVowels = (s) => {
    const vowels = "aeiouAEIOU";
    let count = 0;

    for (const char of s) {
        if (vowels.includes(char)) {
            count++;
        }
    }

    return count;
};

const s = "Hello World";
console.log(cVowels(s)); 

3

• Define a string containing all vowels.
• Loop through the input string and check if each character is a vowel using includes().
• Increment the counter for every match.

2. Using Regular Expression

Using a regex pattern is a compact and efficient way to count vowels in a string.

const cVowels = (s) => {
    const matches = s.match(/[aeiou]/gi);
    return matches ? matches.length : 0;
};

const s = "Hello World";
console.log(cVowels(s));

3

• The regex /[aeiou]/gi matches all vowels (a, e, i, o, u) in a case-insensitive manner (i) and globally (g).
• Use the match method to find all matches.
• Return the length of the matches array or 0 if no matches are found.

3. Using reduce() and indexOf() Methods

This method uses the reduce() function to iterate over the string while checking if a character is a vowel.

const cVowels = (s) => {
    const vowels = "aeiouAEIOU";
    return [...s].reduce((count, char) => 
        vowels.indexOf(char) !== -1 ? count + 1 : count, 0);
};

const s = "Hello World";
console.log(cVowels(s)); 

3

• Spread the string into an array of characters.
• Use reduce() to accumulate the count.
• Check if each character exists in the vowels string using indexOf.

4. Using split() and Array.includes() Methods

This method uses split() to create an array of characters and includes() to check for vowels.

const cVowels = (s) => {
    const vowels = ["a", "e", "i", "o", "u", "A", "E", "I", "O", "U"];
    return s.split("").filter(char => vowels.includes(char)).length;
};

const s = "Hello World";
console.log(cVowels(s));

3

• Split the string into an array of characters.
• Use filter() to keep only characters that are vowels.
• Return the length of the filtered array.

5. Using a Map

This approach uses a Map to store vowels as keys for faster lookup.

const cVowels = (s) => {
    const vowelsMap = new Map([
        ["a", true], ["e", true], ["i", true], ["o", true], ["u", true],
        ["A", true], ["E", true], ["I", true], ["O", true], ["U", true]
    ]);

    let count = 0;
    for (const char of s) {
        if (vowelsMap.has(char)) {
            count++;
        }
    }
    return count;
};

const s = "Hello World";
console.log(cVowels(s));

3

• Create a Map with all vowels as keys for quick lookup.
• Iterate through the string using a for...of loop.
• Increment the count for each vowel found in the Map.

Which Approach Should You Use?