How to add timestamp in firebase realtime database - ionic 2

Hi Guys, how I can add timestamp in firebase?
client and server must have the same time. I tried to googled it but I can’t work it out. below is my code

public outlet_id = “outlet1”;
constructor(public navCtrl: NavController, private angFire: AngularFire) {
this.displays = angFire.database.list(’/Projectors/displays/outlets/’+this.outlet_id);

let objTimestamp = {timestamp: firebase.database.ServerValue.TIMESTAMP};
Object.assign(project, objTimestamp);