【面试题】面试官问：如果有100个请求，你如何使用Promise控制并发？

const urls = ["url1", "url2", ... ,"url100"]; 
const maxConcurrentNum = 10; // 最大并发数 
// 数组分块，chunk表示每批次数量，返回数组二维数组 
function chunk(arr, chunk) { 
  let result = []; 
  for (let i = 0, len = arr.length; i < len; i += chunk) { 
    result.push(arr.slice(i, i + chunk)); 
   } 
   return result; 
 }
// 异步请求方法 
function fetchUrl(url) { 
  return new Promise((resolve, reject) => { 
    fetch(url) 
      .then(res => resolve(res)) 
      .catch(err => reject(err)); 
     }); 
   }
// 对url数组进行分块处理
const chunkedUrls = chunk(urls, maxConcurrentNum);
(async function () {
  try {
    for (let urls of chunkedUrls) {
      const promises = urls.map(url => fetchUrl(url));
      // 等待所有promises完成执行，并将结果存入results数组中
      const results = await Promise.all(promises);
      console.log('results:', results);
    }
  } catch (err) {
   console.error(err);
  }
})();

const promiselist = [];
for (let i = 0; i < 100; i++) {
  const promise = fetch(`https://example.com/data${i}.json`);
  promiselist.push(promise);
}
Promise.race(promiselist)
  .then(response => {
    // handle the fastest response here
  })
  .catch(error => {
    console.error(error);
  });

async function getData() {
  const promiselist = [];
  for (let i = 0; i < 100; i++) {
    const promise = fetch(`https://example.com/data${i}.json`);
    promiselist.push(promise);
  }
  const responses = await Promise.all(promiselist);
  for (const response of responses) {
    // handle each response here 
  }
}
getData().catch(error => {
  console.error(error);
});

async function getData() {
  const promiselist = [];
  for (let i = 0; i < 100; i++) {
    const promise = fetch(`https://example.com/data${i}.json`);
    promiselist.push(promise);
  }
  const response = await Promise.race(promiselist);
  // handle the fastest response here
}
getData().catch(error => {
  console.error(error);
});

function getData() {
 const limit = 5; // maximum concurrent requests
 const dataUrls = ['https://example.com/data1.json', 
                   'https://example.com/data2.json',
                   'https://example.com/data3.json',
                   'https://example.com/data4.json',
                   'https://example.com/data5.json',
                   'https://example.com/data6.json'];
 let counter = 0;
 const getDataPromise = dataUrl => {
   return new Promise((resolve, reject) => {
     fetch(dataUrl)
       .then(response => {
         counter--;
         resolve(response);
       })
       .catch(error => {
         counter--;
         reject(error);
       });
   });
 };
 const getDataPromises = dataUrls.map(dataUrl => {
   if (counter < limit) {
     counter++;
     return getDataPromise(dataUrl);
   } else {
     return new Promise(resolve => {
       const interval = setInterval(() => {
         if (counter < limit) {
           counter++;
           clearInterval(interval);
           resolve(getDataPromise(dataUrl));
         }
       }, 100);
     });
   }
 });
 Promise.all(getDataPromises)
   .then(responses => {
     for (const response of responses) {
       // handle each response here
     }
   })
   .catch(error => {
     console.error(error);
   });
}
getData();