const array = [3, 'a', 'a', 'a', 2, 3, 'a', 3, 'a', 2, 4, 9, 3];

const getMostFrequentValue = array => {
  const countAllValues = array.reduce((acc, curr) => {
    if (curr in acc) {
      return { ...acc, [curr]: acc[curr] + 1 }
    }

    return { ...acc, [curr]: 1 }
  }, {})
  const countedValues = Object.entries(countAllValues);
  return countedValues.reduce((acc, [key, value], idx) => {
    if (value === countAllValues[key]) {
      return `item ${key} ${value} times`;
    }
    return acc;
  }, {});
}

console.log(getMostFrequentValue(array));