js中的iterator

// 内置迭代器示例
const arr = [1, 2, 3];
const iterator = arr[Symbol.iterator]();

console.log(iterator.next()); // {value: 1, done: false}
console.log(iterator.next()); // {value: 2, done: false}
console.log(iterator.next()); // {value: 3, done: false}
console.log(iterator.next()); // {value: undefined, done: true}

// 自定义迭代器示例
class Counter {
  constructor(limit) {
    this.limit = limit;
  }

  [Symbol.iterator]() {
    let count = 1;
    const limit = this.limit;
    return {
      next() {
        if (count <= limit) {
          return { value: count++, done: false };
        } else {
          return { value: undefined, done: true };
        }
      }
    };
  }
}

const counter = new Counter(3);
for (const num of counter) {
  console.log(num); // 1, 2, 3
}

function safeIterate(iterable) {
  if (iterable && typeof iterable[Symbol.iterator] === 'function') {
    for (const item of iterable) {
      console.log(item);
    }
  } else {
    console.log('无法迭代');
  }
}

safeIterate([]); // 输出: 无法迭代
safeIterate([1, 2, 3]); // 输出: 1, 2, 3