Array.prototype.myMap = function(callback) {
  const result = [];
  for (let i = 0; i < this.length; i++) {
    result.push(callback(this[i], i, this));
  }
  return result;
};

Array.prototype.myMap = function(callback) {
  return callback(...this);
};

Array.prototype.myMap = function(callback) {
  for (let i = 0; i < this.length; i++) {
    this[i] = callback(this[i]);
  }
};

Array.prototype.myMap = function(callback) {
  const result = [];
  this.forEach((item) => result.push(callback(item)));
  return result;
};