map.js

// ASSERT
const eqArrays = function(arrOne, arrTwo) {
  if (arrOne.length !== arrTwo.length) {
    return false;
  }
  for (i = 0; i < arrOne.length; i++) {
    if (arrOne[i] !== arrTwo[i]) {
      return false;
    }
  }
  return true;
};

const assertArraysEqual = function(actual, expected) {
  if (eqArrays(actual, expected)) {
    console.log(`✅✅✅ Assertion Passed: ${(actual)} === ${(expected)}`);
  } else {
    console.log(`🛑🛑🛑 Assertion Failed: ${(actual)} !== ${(expected)}`);
  }
};

// ACTUAL FUNCTION
const words = ["ground", "control", "to", "major", "tom"];
const map = function(array, callback) {
  const results = [];
  for (let item of array) {
    results.push(callback(item));
  }
  return results;
};

const results1 = map(words, word => word[0]);
assertArraysEqual(results1, ['g', 'c', 't', 'm', 't']);

const results2 = map(words, word => word.length);
assertArraysEqual(results2, [6, 7, 2, 5, 3]);

const results3 = map(words, word => word[5]);
assertArraysEqual(results3, ['d', 'o', undefined, undefined, undefined]);