如何使用for循环实现map()函数？

function map(arr, callback) {
  var result = [];
  for (var i = 0; i < arr.length; i++) {
    result.push(callback(arr[i], i, arr));
  }
  return result;
}

// 示例用法
var numbers = [1, 2, 3, 4, 5];
var doubledNumbers = map(numbers, function(num) {
  return num * 2;
});
console.log(doubledNumbers); // 输出 [2, 4, 6, 8, 10]

function map(obj, callback) {
  var result = {};
  for (var key in obj) {
    if (obj.hasOwnProperty(key)) {
      result[key] = callback(obj[key], key, obj);
    }
  }
  return result;
}

// 示例用法
var person = {
  name: 'John',
  age: 30,
  city: 'New York'
};
var modifiedPerson = map(person, function(value) {
  return value.toUpperCase();
});
console.log(modifiedPerson); // 输出 { name: 'JOHN', age: '30', city: 'NEW YORK' }