mostCommon.js

const mostCommon = (arrayOfStrings) => {
  const map = {};
  let maxFreqCount = 0;
  let maxFreqString = arrayOfStrings[0];

  let output = "";

  if (arrayOfStrings.length === 0) {
    output = `"Sorry. The input array is empty"`;
  } else {
    for (let index = 0; index < arrayOfStrings.length; index++) {
      const element = arrayOfStrings[index];

      if (map[element]) {
        map[element]++;
      } else {
        map[element] = 1;
      }

      if (map[element] > maxFreqCount) {
        maxFreqCount = map[element];
        maxFreqString = element;
      }
    }

    output = maxFreqString;
  }

  return output;
};

const inputArrayOfStrings1 = ["j", "k", "k", "l", "m", "n", "o"];
const inputArrayOfStrings2 = ["ijk", "ijk", "xyz", "xyz", "ijk", "opr", "stu"];
const inputArrayOfStrings3 = [];

const output1 = mostCommon(inputArrayOfStrings1);
const output2 = mostCommon(inputArrayOfStrings2);
const output3 = mostCommon(inputArrayOfStrings3);

console.log(`Input string: ${inputArrayOfStrings1}. Result: ${output1}`);
console.log(`Input string: ${inputArrayOfStrings2}. Result: ${output2}`);
console.log(`Input string: ${inputArrayOfStrings3}. Result: ${output3}`);