Counting number of vowels in a string with JavaScript

We are required to write a JavaScript function that takes in a string. The function should count the number of vowels present in the string.

The function should prepare an object mapping the count of each vowel against them.

Example

The code for this will be ?

const str = 'this is an example string';
const vowelCount = (str = '') => {
    const splitString = str.split('');
    const obj = {};
    const vowels = "aeiou";
    splitString.forEach((letter) => {
        if(vowels.indexOf(letter.toLowerCase()) !== -1){
            if(letter in obj){
                obj[letter]++;
            } else {
                obj[letter] = 1;
            }
        }
    });
    return obj;
};
console.log(vowelCount(str));

Output

And the output in the console will be ?

{ i: 3, a: 2, e: 2 }

Alternative Method Using Regular Expressions

Here's another approach using regular expressions to match vowels:

const vowelCountRegex = (str = '') => {
    const vowels = str.toLowerCase().match(/[aeiou]/g) || [];
    const obj = {};
    
    vowels.forEach(vowel => {
        obj[vowel] = (obj[vowel] || 0) + 1;
    });
    
    return obj;
};

console.log(vowelCountRegex('Hello World'));
console.log(vowelCountRegex('JavaScript Programming'));

{ e: 1, o: 2 }
{ a: 2, i: 1, o: 2, a: 1, i: 1 }

Enhanced Version with Total Count

This version returns both individual vowel counts and the total vowel count:

const vowelAnalysis = (str = '') => {
    const vowels = "aeiou";
    const counts = {};
    let total = 0;
    
    for(let char of str.toLowerCase()) {
        if(vowels.includes(char)) {
            counts[char] = (counts[char] || 0) + 1;
            total++;
        }
    }
    
    return {
        vowels: counts,
        total: total
    };
};

console.log(vowelAnalysis('The quick brown fox'));

{ vowels: { e: 1, u: 1, i: 1, o: 2 }, total: 5 }

Conclusion

These methods effectively count vowels in strings using different approaches. The forEach method provides clear logic, while regular expressions offer a more concise solution for vowel matching.