js list map 遍历

// 基本用法
const numbers = [1, 2, 3, 4];
const doubled = numbers.map(function(num) {
  return num * 2;
});
console.log(doubled); // 输出: [2, 4, 6, 8]

// 使用箭头函数简化代码
const doubledWithArrow = numbers.map(num => num * 2);
console.log(doubledWithArrow); // 输出: [2, 4, 6, 8]

// 提取对象数组中的某个属性
const people = [
  { name: 'Alice', age: 21 },
  { name: 'Bob', age: 24 },
  { name: 'Charlie', age: 27 }
];
const names = people.map(person => person.name);
console.log(names); // 输出: ['Alice', 'Bob', 'Charlie']

// 错误的示例：没有返回值
const numbers = [1, 2, 3];
const wrongResult = numbers.map(function(num) {
  num * 2; // 缺少 return
});
console.log(wrongResult); // 输出: [undefined, undefined, undefined]

// 正确的示例：确保有返回值
const correctResult = numbers.map(function(num) {
  return num * 2;
});
console.log(correctResult); // 输出: [2, 4, 6]