Return Vowels in a string in JavaScript

We are required to write a JavaScript function that takes in a string that might contain some alphabets. The function should count and return the number of vowels that exists in the string.

Syntax

function countVowels(str) {
    // Convert to lowercase for case-insensitive comparison
    // Loop through each character
    // Check if character is a vowel (a, e, i, o, u)
    // Return the count
}

Example: Using for Loop

Following is the code ?

const str = 'this is a string';

const countVowels = (str = '') => {
    str = str.toLowerCase();
    const legend = 'aeiou';
    let count = 0;
    
    for(let i = 0; i < str.length; i++){
        const el = str[i];
        if(!legend.includes(el)){
            continue;
        }
        count++;
    }
    return count;
};

console.log(countVowels(str));
console.log(countVowels('Hello World'));
console.log(countVowels('JavaScript'));

Output

Following is the output on console ?

4
3
3

Using Regular Expressions

A more concise approach using regular expressions:

const countVowelsRegex = (str = '') => {
    const matches = str.toLowerCase().match(/[aeiou]/g);
    return matches ? matches.length : 0;
};

console.log(countVowelsRegex('this is a string'));
console.log(countVowelsRegex('Hello World'));
console.log(countVowelsRegex('bcdfg'));

4
3
0

Using Array Methods

Using modern JavaScript array methods for a functional approach:

const countVowelsArray = (str = '') => {
    const vowels = 'aeiou';
    return str.toLowerCase()
              .split('')
              .filter(char => vowels.includes(char))
              .length;
};

console.log(countVowelsArray('this is a string'));
console.log(countVowelsArray('Programming'));
console.log(countVowelsArray('xyz'));

4
3
0

Comparison

Conclusion

Use the for loop method for performance-critical applications, or the regex approach for cleaner, more readable code. All methods handle case-insensitive vowel counting effectively.