task_scheduler/modules/rpc/index.ts

import { TaskSchedulerService, TaskSchedulerServiceClient } from './rpc';

export * from './rpc';

/**
 * GetTaskSchedulerService returns an TaskSchedulerService implementation
 * which dispatches events indicating when requests have started and ended.
 *
 * @param ele The parent element, used to dispatch events.
 */
export function GetTaskSchedulerService(
  ele: HTMLElement
): TaskSchedulerService {
  const host = `${window.location.protocol}//${window.location.host}`;
  const rpcClient: TaskSchedulerService = new TaskSchedulerServiceClient(
    host,
    window.fetch.bind(window)
  );
  const handler = {
    get(target: any, propKey: any, receiver: any) {
      const origMethod = target[propKey];
      return function (...args: any[]) {
        ele.dispatchEvent(new CustomEvent('begin-task', { bubbles: true }));
        return origMethod
          .apply(rpcClient, args)
          .then((v: any) => {
            ele.dispatchEvent(new CustomEvent('end-task', { bubbles: true }));
            return v;
          })
          .catch((err: any) => {
            ele.dispatchEvent(
              new CustomEvent('fetch-error', {
                detail: {
                  error: err,
                  loading: propKey,
                },
                bubbles: true,
              })
            );
            Promise.reject(err);
          });
      };
    },
  };
  return new Proxy(rpcClient, handler);
}