// 实现简单的请求队列
class RequestQueue {
  constructor(maxConcurrent = 4) {
    this.maxConcurrent = maxConcurrent;
    this.queue = [];
    this.activeCount = 0;
  }

  add(requestFn) {
    return new Promise((resolve, reject) => {
      this.queue.push({ requestFn, resolve, reject });
      this.next();
    });
  }

  next() {
    if (this.activeCount < this.maxConcurrent && this.queue.length) {
      const { requestFn, resolve, reject } = this.queue.shift();
      this.activeCount++;
      
      requestFn()
        .then(resolve)
        .catch(reject)
        .finally(() => {
          this.activeCount--;
          this.next();
        });
    }
  }
}

// 使用示例
const queue = new RequestQueue(4);

function makeRequest(url) {
  return () => fetch(url).then(res => res.json());
}

// 添加多个请求
queue.add(makeRequest('/api/data1')).then(data => console.log(data));
queue.add(makeRequest('/api/data2')).then(data => console.log(data));
// ...更多请求

// 使用AbortController取消之前的请求
let controller;

async function fetchData(query) {
  // 取消之前的请求
  if (controller) {
    controller.abort();
  }
  
  controller = new AbortController();
  
  try {
    const response = await fetch(`/api/search?q=${query}`, {
      signal: controller.signal
    });
    const data = await response.json();
    // 处理数据
  } catch (err) {
    if (err.name !== 'AbortError') {
      console.error('请求失败:', err);
    }
  }
}