<a (click)="check()"> click </a>

constructor(private _e: ElectronService) { }

check () {
   this._e.ipcRenderer.send ('conn', 'round');
   this._e.ipcRenderer.on ('conn-st', (event, args) => {
      console.log (args);
   });
}

ipcMain.on ('conn', function (event, args) {
  event.sender.send ('conn-st', 'trip');
});

(node:23006) Error: Possible EventEmitter memory leak detected. 11 conn-st listeners added. Use emitter.setMaxListeners() to increase limit

// Create a listener.
var myListener = ipcRenderer.on("channel", function (event, args) {});
// Delete only this one by its ID:
ipcRenderer.removeListener("channel", myListener);

// Create a few listeners.
var myListener0 = ipcRenderer.on("channel", function (event, args) {});
var myListener1 = ipcRenderer.on("channel", function (event, args) {});
var myListener2 = ipcRenderer.on("channel", function (event, args) {});
var myListener3 = ipcRenderer.on("channel", function (event, args) {});

// Delete all listeners for socket "channel".
ipcRenderer.removeAllListeners("channel");