如何为角度5 / nodejs启用Access-Control-Allow-Origin？

Question

阅读包括“ Access-Control-Allow-Origin”在内的许多方法，但没有一种对我有用。

我使用@ angular / common / http模块和外部url作为数据源。通过尝试获取数据来获取错误：///// .................

Failed to load http://accounts.......com/accounts: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:4200' is therefore not allowed access. The response had HTTP status code 503.

account.service.ts：

Failed to load http://accounts.......com/accounts: No 'Access-Control-Allow-Origin' header is present on the requested resource. Origin 'http://localhost:4200' is therefore not allowed access. The response had HTTP status code 503.

app.module.ts

import { Injectable                    } from '@angular/core';
import { Router                        } from '@angular/router';
import { HttpClient, HttpParams        } from '@angular/common/http';
import { HttpHeaders                   } from '@angular/common/http';

import { Observable                    } from 'rxjs';
import { catchError                    } from 'rxjs/operators';

import { Account                       } from '../models/account';

const baseUrl     : string = 'http://accounts..................com/';
const httpOptions : any    = {
  headers: new HttpHeaders({
    //'Content-Type':  'application/json',
    'Access-Control-Allow-Headers': 'Content-Type',
    'Access-Control-Allow-Methods': 'GET',
    'Access-Control-Allow-Origin': '*'
  })
};

@Injectable()
export class AccountService {
  private isUserLoggedIn;
  private usreName;
  private account : Account;

  constructor(
    private http: HttpClient,
    private router: Router
  ) {}

  logIn (credentials: any): Observable<Account> {
    return this.http.get<Account>(baseUrl + 'accounts');
  }
}

请帮忙

////////////////已尝试修复1

import { BrowserModule                 } from '@angular/platform-browser';
import { HttpClientModule              } from '@angular/common/http';
import { NgModule                      } from '@angular/core';

import { routing                       } from './routing';
import { AppComponent                  } from './app.component';
import { AppGlobal                     } from './app.global';

import { AccountComponent              } from './components/account/account.component';

@NgModule({
  declarations  : [
    AppComponent,
    AccountComponent,
    ....
  ],
  imports       : [
    routing,
    BrowserModule,
    HttpClientModule,
    CookieModule.forRoot()
  ],
  providers     : [AccountService, AppGlobal],
  bootstrap     : [AppComponent]
})
export class AppModule { }

我仍然收到该错误：

对预检请求的响应未通过访问控制检查：在所请求的资源上不存在“ Access-Control-Allow-Origin”标头。因此，不允许访问源' http：// localhost：4200 '。响应的HTTP状态码为503。

///////////////尝试修复2

proxy.conf.json：

//......
import { HttpHeaders} from '@angular/common/http';
//.......
logIn (credentials: any): Observable<Account> {

    const headers = new HttpHeaders()
      .append('Content-Type', 'application/json')
      .append('Access-Control-Allow-Headers', 'Content-Type')
      .append('Access-Control-Allow-Methods', 'GET')
      .append('Access-Control-Allow-Origin', '*');
    return this.http.get<Account>(baseUrl + 'accounts',  {headers});
}

ng serve --proxy-config proxy.conf.json

也错误

Answer 1

**设置标头以允许Express中的CORS来源**

=>在server.js文件或邮件文件中添加代码。

app.use(function(req, res, next) {
   res.header("Access-Control-Allow-Origin", "*");
   res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
  next();
 });

CORS（跨源资源共享）是一种HTML5功能，即使一个站点使用不同的域名，它也允许一个站点访问另一站点的资源。

实际上，CORS的W3C规范在提供响应标头的一些简单示例方面做得很好，例如密钥标头，Access-Control-Allow-Origin以及在Web服务器上启用CORS必须使用的其他标头。