countOnly.js

const assertEqual = function(actual, expected) {
  if (actual === expected) {
    console.log(`The '${actual}' and the '${expected}' are the same✅`);
  } else console.assert(actual === expected, "❌");
};

const countOnly = function (allItems , itemsToCount) {
  const results = {};

  for (const item of allItems) {
    if (itemsToCount[item]){
      if (results[item]) {
       results[item] += 1;
     } else {
       results[item] = 1;
    }
    console.log(item);
   };
  };
    

  return results;
}

const firstNames = [
  "Karl",
  "Salima",
  "Agouhanna",
  "Fang",
  "Kavith",
  "Jason",
  "Salima",
  "Fang",
  "Joe"
];

const result1 = countOnly(firstNames, { "Jason": true, "Karima": true, "Fang": true, "Agouhanna": false });

assertEqual(result1["Jason"], 1);
assertEqual(result1["Karima"], undefined);
assertEqual(result1["Fang"], 2);
assertEqual(result1["Agouhanna"], undefined);