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function map(arr, yourFunction) {
  const resultsArray = [];

  for (let i = 0; i < arr.length; i++) {
    resultsArray.push(yourFunction(arr[i], i));
  }

  return resultsArray;
}

const numArray = [1, 2, 3];

const results = map(numArray, (item) => item * 2);

console.log(results);