countOnly.js

const assertEqual = function(actual, expected) {
  if (actual === expected) {
    console.log(`✔✔ Assertion Passed: ${actual} === ${expected}`);
  } else if (actual !== expected) {
    console.log(`❌ Assertion Failed: ${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
      }
    }
  }
  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);