basic interceptor for fetch. assumes your routes are proxy through `/api-`

fetch-interceptors.ts

interface Interceptors {
  request: { [k: string]: (...args: any[]) => any };
  response: { [k: string]: (response: Response) => any };
}

class Interceptor {
  protected requestCount: number = 0;
  protected interceptors: Interceptors = {
    request: {},
    response: {},
  };

  private runInterceptors(type: keyof Interceptors, args: any | Response) {
    const typeInterceptors = this.interceptors[type];

    if (!typeInterceptors) {
      return;
    }

    const keys = Object.keys(typeInterceptors);

    keys.forEach((key: string) => {
      typeInterceptors[key](args);
    });
  }

  public registerInterceptor(name: string, type: keyof Interceptors,  fn: any) {
    if (!this.interceptors[type][name]) {
      this.interceptors[type][name] = fn;
    }
  }

  public init() {
    const { fetch } = window;

    window.fetch = (...args: any[]) => {
      const url = args[0];

      /**
       * @note we can assume that all client side requests will be done with a /api proxy
       * only requests that will not have this are GQL requests. should change this to run through
       * /api-graphql
       */
      const apiRx = /\/api-(.*)/;

      if (url.match(apiRx)) {
        this.runInterceptors('request', args);
      }

      return fetch.apply(window, args).then((response: Response) => {
        if (url.match(apiRx)) {
          this.runInterceptors('response', response);
        }

        return response;
      });
    };
  }
}

export default new Interceptor();