JavaScript前端控制网络并发数目的常见方法小结

class PromiseQueue {
  constructor(maxConcurrent) {
    this.maxConcurrent = maxConcurrent;
    this.queue = [];
    this.currentCount = 0;
  }

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

  tryToRun() {
    if (this.queue.length === 0 || this.currentCount >= this.maxConcurrent) {
      return;
    }
    this.currentCount++;
    const { promiseCreator, resolve, reject } = this.queue.shift();
    promiseCreator().then(resolve, reject).finally(() => {
      this.currentCount--;
      this.tryToRun();
    });
  }
}

// 实例化队列，设置最大并发数为 2
const queue = new PromiseQueue(2);

// 添加请求到队列
queue.add(() => fetch(url1)).then(handleResponse);
queue.add(() => fetch(url2)).then(handleResponse);
queue.add(() => fetch(url3)).then(handleResponse);

import pLimit from 'p-limit';

const limit = pLimit(2);

const input = [
    limit(() => fetch(url1)),
    limit(() => fetch(url2)),
    limit(() => fetch(url3)),
    limit(() => fetch(url4)),
];

// 只有 2 个请求被同时处理
Promise.all(input).then(results => {
    // 处理结果
});

const MAX_CONCURRENT = 2;
let concurrentCount = 0;
const xhrPool = [];

function fetchWithXhr(url) {
    if (concurrentCount >= MAX_CONCURRENT) {
        setTimeout(() => fetchWithXhr(url), 200); // 200ms 后重试
        return;
    }
    concurrentCount++;
    const xhr = new XMLHttpRequest();
    xhr.open("GET", url);
    xhr.onload = () => {
        handleResponse(xhr.response);
        concurrentCount--;
        if (xhrPool.length > 0) {
            const newXhr = xhrPool.shift();
            fetchWithXhr(newXhr.url);
        }
    };
    xhr.onerror = xhr.onabort = () => {
        concurrentCount--;
    };
    xhr.send();
}

function abortExtraRequests() {
    while (concurrentCount > MAX_CONCURRENT) {
        const xhrToAbort = xhrPool.pop();
        xhrToAbort.abort();
    }
}

// 发起请求
fetchWithXhr("https://api.example.com/data1");
fetchWithXhr("https://api.example.com/data2");
fetchWithXhr("https://api.example.com/data3");

const MAX_CONCURRENT = 2;
let concurrentCount = 0;
const controllerQueue = new Map();

async function fetchWithAbortController(url) {
    if (concurrentCount >= MAX_CONCURRENT) {
        await new Promise(resolve => setTimeout(resolve, 200)); // 200ms 后重试
        return fetchWithAbortController(url);
    }

    const controller = new AbortController();
    concurrentCount++;
    controllerQueue.set(url, controller);

    try {
        const response = await fetch(url, { signal: controller.signal });
        handleResponse(await response.json());
    } catch (error) {
        // 错误处理
    } finally {
        controllerQueue.delete(url);
        concurrentCount--;
        if (__yourCondition) {
            controllerQueue.get(__specificUrl).abort(); // 取消下一个请求
        }
    }
}

// 发起请求
fetchWithAbortController("https://api.example.com/data1");
fetchWithAbortController("https://api.example.com/data2");
fetchWithAbortController("https://api.example.com/data3");