在 Angular 6 中按顺序执行 http 请求 [英] Execute http request sequentially in Angular 6

问题描述

我需要依次向服务器发送多个HTTP PUT请求(在完成上一个请求后才开始下一个请求，请求数量不固定).如果我使用以下源代码，将发送所有请求

I need to send multiple HTTP PUT request to server sequentially (after the next request is only started after completing the previous request, the number of request is not fixed). If I use the below source code, all request will be sent

 `listURL.forEach(url => {
    const req = new HttpRequest('PUT', url, formData, { reportProgress: true});
    httpClient.request(req).subscribe(event=>{});
  });`

有没有办法按顺序执行请求?

Is there anyway to execute the requests sequentially?

推荐答案

如果你不熟悉 rxjs，或许你可以试试下面的方法?

If you are not familiar with rxjs, perhaps you can try the following?

let requests = listURL.map(url => new HttpRequest('PUT', url, formData, { reportProgress: true});

function do_seq(i) {
  httpClient.request(requests[i]).subscribe(event => {
   if (i < requests.length - 1) do_seq(i + 1);
  });
 }

do_seq(0);

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