Sometimes, we want to count the frequency of characters in a string using JavaScript.

In this article, we’ll look at how to count the frequency of characters in a string using JavaScript.

How to count the frequency of characters in a string using JavaScript?

To count the frequency of characters in a string using JavaScript, we can use the spread operator and the array reduce method.

For instance, we write:

const counter = str => {
  return [...str].reduce((total, letter) => {
    if (!total[letter]) {
      return {
        ...total,
        [letter]: 1
      }
    } else {
      return {
        ...total,
        [letter]: total[letter] + 1
      }
    }
  }, {});
};

console.log(counter("aabsssd"));

to define the counter function that spreads the string to a character array.

Then we call reduce on the array with a callback that checks whether total[letter] already exists.

If it doesn’t exist, we add the [letter] property and set it to 1.

Otherwise, we increment total[letter] by 1 and return that object.

We set total to an empty object as its initial value by setting that as the 2nd argument of reduce.

Therefore, the console log logs

{
  a: 2,
  b: 1,
  d: 1,
  s: 3
}

Conclusion

To count the frequency of characters in a string using JavaScript, we can use the spread operator and the array reduce method.