javascript - 添加计时器到 Promise.all、map

Question

我想在下面的获取请求之间添加一些超时。我的意思是，流程应该如下所示: timeout, https://example.com/example1, timeout, https://example.com/example2, timeout, https://example.com/example3, timeout 等(或者没有第一次超时，无论如何)。

以下功能正常工作:

function promiseGetInformationFromMultipleUrls(parts) {
    return Promise.all(parts.map(part => {
      return request({
            'url': `https://example.com/${part}`,
            'json': true
        }).then(partData =>  {console.log("Part data was fetched: " + part); return partData.result;})
          .catch(err => {console.error("Error during fetching data from part: " + part + ", error code: " + err.statusCode);});
    }));
}

其中部分是 -> example1、example2、example3...

我正在尝试通过添加计时器来做到这一点:

const timer = ms => new Promise( res => setTimeout(res, ms));

并使用它:

function promiseGetInformationFromMultipleUrls(parts) {
    return Promise.all(parts.map(part => {
    console.log("wait 1 seconds");
    timer(1000).then(_=>console.log("done"));
      return request({
            'url': `https://example.com/${part}`,
            'json': true
        }).then(partData =>  {console.log("Part data was fetched: " + part); return partData.result;})
          .catch(err => {console.error("Error during fetching data from part: " + part + ", error code: " + err.statusCode);});
    }));
}

但这是错误的流程 -> 超时，超时，超时，...，获取请求1，获取请求2，获取请求3。

Answer 1

您可以将其简化为 Promise 链:

function promiseGetInformationFromMultipleUrls(parts) {
 return parts.reduce((chain, part) =>
  chain.then((result) =>
    timer(1000).then(() => 
      request(/*...*/).then(res => 
        result.concat(res)
      )
    )
  ),
  Promise.resolve([])
);
}

但是这很丑陋，所以你可以使用 async/wait 来代替:

 async function promiseGetInformationFromMultipleUrls(parts){
   const result = [];
   for(const part of parts){
     await timer(1000);
     result.push(await request(/*...*/));
  }
  return result;
}