javascript - CORS 错误 : “requests are only supported for protocol schemes: http…” etc

Question

我正在尝试运行一个简单的应用程序。我有一个 Express 后端，它在访问 localhost:4201/ticker 时返回一个 JSON 字符串。当我运行服务器并通过 http 从我的 Angular 服务向此链接发出请求时，我收到以下错误:

XMLHttpRequest cannot load localhost:4201/ticker. Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, https.

我阅读了以下文章:Understanding and Using CORS如前所述，在我的快速服务器上使用了 cors 模块。但是，我仍然收到上面给出的错误。部分代码如下:

服务器代码:

private constructor(baseUrl: string, port: number) {
    this._baseUrl = baseUrl;
    this._port = port;
    this._express = Express();
    this._express.use(Cors());
    this._handlers = {};
    this._hInstance = new Handlers();
    this.initHandlers();
    this.initExpress();
}
private initHandlers(): void {
    // define all the routes here and map to handlers
    this._handlers['ticker'] = this._hInstance.ticker;
}
private initExpress(): void {
    Object.keys(this._handlers)
        .forEach((key) => {
            this._express.route(this._url(key))
                .get(this._handlers[key]);
        });
}
private _url(k: string): string {
    return '/' + k;
}

这是处理函数:

ticker(req: Request, res: Response): void {
    Handlers._poloniex
        .getTicker()
        .then((d) => {
            return Filters.tickerFilter(d, Handlers._poloniex.getBases());
        })
        .then((fdata) => {

            //res.header('Access-Control-Allow-Origin', "*");
            //res.header("Access-Control-Allow-Headers", "Origin, X-Requested-With, Content-Type, Accept");
            res.header('Content-Type', 'application/json');
            res.send(JSON.stringify(fdata));
        })
        .catch((err) => {
           this._logger.log([
                'Error: ' + err.toString(),
                'File: ' + 'handlers.class.ts',
                'Method: ' + 'ticker'
            ], true);
        });   
}

这是我的 Angular 服务:

export class LiveTickerService {

  private _baseUrl: string;
  private _endpoints: {[key:string]: string};

  constructor(
    private _http: Http
  ) {
    this._baseUrl = 'localhost:4201/';
     this._endpoints = {
       'ticker': 'ticker'
     };
   }

  getTickerData(): Observable<Response> {
    return this._http.get(this._baseUrl + this._endpoints['ticker'])
      .map(resp => resp.json())
  }

}

以下是我如何使用我的服务:

getTicker() {
  let a = new Array<{[key: string]: any}>();
  this._tickerService.getTickerData()
     .subscribe(
        data => {
          let parsed = JSON.parse(JSON.stringify(data));
          Object.keys(parsed)
            .forEach((k) => {
              a.push({k: parsed[k]});
            });
         this.data = a;
        },
        error => console.log(error.toString()),
        () => console.log('Finished fetching ticker data')
      );
  return this.data;
}

Answer 1

XMLHttpRequest cannot load localhost:4201/ticker. Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, https.

每当您看到“仅支持协议(protocol)方案” 消息时，几乎可以肯定这意味着您只是忘记了输入 https 或 http 在您的代码中的请求 URL 上。

所以在这种情况下，解决方法是在此处的代码中使用 URL http://localhost:4201/ticker:

this._baseUrl = 'http://localhost:4201/';

...因为没有 http://，localhost:4201/ticker 并不是您真正想要的 URL。