允许使用Express JS和HTML5 fetch()进行跨域请求 [英] Allowing cross domain requests with Express JS and HTML5 fetch()

问题描述

如何通过ExpressJS服务器和Javascript的提取来允许跨域请求?我认为客户端的fetch()可能是个问题，因为Access-Control-Allow-Origin: *在响应的标题中.

How can I allow cross domain requests with an ExpressJS server and Javascript's fetch? I think this might be an issue with fetch() from the client because Access-Control-Allow-Origin: * is in the response's headers.

我添加了以下代码，但仍然无法正常工作:

I added this code but it still doesn't work:

app.use(function(req, res, next) {
    res.header("Access-Control-Allow-Origin", "localhost:4200"); // update to match the domain you will make the request from
    res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
    next();
});

我注意到请求标头不包含有关COR的任何内容:

I noticed the request headers don't include anything about COR:

Accept  
text/html,application/xhtml+xm…plication/xml;q=0.9,*/*;q=0.8
Accept-Encoding 
gzip, deflate
Accept-Language 
en-US,en;q=0.5
Cache-Control   
max-age=0
Connection  
keep-alive
Host    
localhost:4200
If-None-Match   
W/"2ef-TFWfb4ktmG8ds+qhoRRzEvmkPdY"
Upgrade-Insecure-Requests   
1
User-Agent  
Mozilla/5.0 (Windows NT 10.0; …) Gecko/20100101 Firefox/68.0

前端代码:

export function createHttpObservable(url: string) {

    return Observable.create(observer => {

      fetch(url, {mode: 'cors'})
        .then(response => {
          return response.json();
        })
        .then(body => {
          observer.next(body);
          observer.complete();
        })
        .catch(error => {
          observer.error(error);
        })

      });

  }

错误:

Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at http://localhost:9000/api/courses. (Reason: CORS header ‘Access-Control-Allow-Origin’ missing).

推荐答案

本地主机URL不正确.请按如下所示进行更改.

The localhost URL is not proper. Please change like below.

app.use(function(req, res, next) {
res.header("Access-Control-Allow-Origin", "http://localhost:4200"); // update to match the domain you will make the request from
res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
next();

});

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