JavaScript Interview Question: Counting vowels

In this article, we have a fun algorithm challenge: vowels.js. It’s a simple problem – count the vowels in a string. Of course, there are multiple solutions to the problem, and we’ll explore two of them below.

Directions

• Write a function that returns the number of vowels used in a string.
• Vowels are the characters ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’.

Difficulty: Easy

This question is quite easy. It might be asked during a junior developer interview.

Solution #1

The first solution we’ll explore is an iterative way to solve this problem. It’s pretty straightforward.

We’ll declare a count variable at the top, which is what we’ll use to keep count of the vowels in the string (str). Next, we’ll want an array of the vowels, which will be used later to compare with the characters (char) in the string (str).

Rather than a traditional for loop, we’re going to use a for of loop. We think it makes the code a bit easier to read and understand.

Notice the method called on str, .toLowerCase(). It’s important not to forget this, else we might end up with an incorrect count (as ‘A’ !== ‘a’).

So, for each character in the string, search for a vowel. If there’s a match, increase the count.

The last step is to actually return the count. We must not forget that!

function vowelCount(str) {
  let count = 0;
  const vowels = ["a", "e", "i", "o", "u"];

  for (let char of str.toLowerCase()) {
    if (vowels.includes(char)) {
      count++;
    }
  }
  return count;
}

console.log(vowelCount("abc")); // 1
console.log(vowelCount("hello")); // 2

Solution #2

This solution is even more straightforward. It makes use of a regular expression, and a ternary operator. It’s storing the regular expression matches (str.match()) in the variable matches. Then it returns the count of matches if there indeed is any, or 0 if there aren’t any matches.

function vowelCount(str) {
  const matches = str.match(/[aeiou]/gi);
  return matches ? matches.length : 0;
}

console.log(vowelCount("abc")); // 1
console.log(vowelCount("hello")); // 2

Conclusion

This challenge is rather simple, but it’s always useful to explore multiple solutions to problems. Feel free to check out some of the other challenges we’ve posted.

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