js控制并发简单写法

不需要获取结果

const tasks = ['url',...];
class Queue {
  constructor(maxConcurrency) {
    this.maxConcurrency = maxConcurrency;
    this.tasks = [];
    this.running = 0;
  }

   run() {
    while (this.running < this.maxConcurrency && this.tasks.length) {
      const task = this.tasks.shift();
      task().then(() => {
        this.running--;
        this.run();
      });

      this.running++;
    }
  }

  enqueue(task) {
    this.tasks.push(task);
    this.run();
  }
}

// 使用示例
const queue = new Queue(3); // 最大并发数为3

for (let i = 0; i < tasks.length; i++) {
  queue.enqueue(() => fetch(tasks[i]).then(res=>res.arrayBuffer()));
}

需要获取结果

// 异步任务数组
class Queue {
  constructor(limit) {
    this.limit = limit
    this.tasks = []
    this.running = 0
    this.results = []
    this.allDoneResolver = null; // 用于解决 allDone promise 的函数
    this.allDone = new Promise(resolve => { // 当所有任务都完成时解决的 promise
      this.allDoneResolver = resolve;
    });
  }

  run() {
    while (this.running < this.limit && this.tasks.length) {
      const task = this.tasks.shift()
      task().then((res) => {
        this.running--
        this.run()
        this.results.push(res)
      })
      this.running++
    }
    if (this.running === 0 && this.tasks.length === 0) { // 所有任务都完成
      this.allDoneResolver(this.results);
    }
  }

  enqueue(task) {
    this.tasks.push(task)
    this.run()

  }

  getResults() {
    return this.allDone; // 返回一个 promise，这个 promise 将在所有任务完成时解决，解决值为所有任务的结果
  }
}




function promiseLimit(urls, limit) {
  return new Promise(resolve => {
    // 使用示例
    const queue = new Queue(limit); // 最大并发数为5

    for (let i = 0; i < urls.length; i++) {
      queue.enqueue(() => fetch(urls[i]).then(res => res.json()));
    }

    // 等待所有任务完成，然后获取结果
    queue.getResults().then((results) => {
      resolve(results)
    });
  })
}

let urls = ['https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json', 'https://res.hc-cdn.com/console-ui/1.25.1.20230925154846/hws/schema.json'];
promiseLimit(urls, 3).then(resList => console.log(resList));
// 并发量限制