Returns the most frequent element in an array.

Use Array.prototype.reduce() to map unique values to an object’s keys, adding to existing keys every time the same value is encountered.
Use Object.entries() on the result in combination with Array.prototype.reduce() to get the most frequent value in the array.


const mostFrequent = arr =>
    arr.reduce((a, v) => {
      a[v] = a[v] ? a[v] + 1 : 1;
      return a;
    }, {})
  ).reduce((a, v) => (v[1] >= a[1] ? v : a), [null, 0])[0];


mostFrequent(['a', 'b', 'a', 'c', 'a', 'a', 'b']); // 'a'