Unique value validation in FormControl of FormArray

I am developing Job form where user can enter his hobbies in the Job Form. I have applied required validation on hobbyName formcontrol, but how can I validate hobby name which should be unique if there is more than one hobby.

Below is my ts code

import { Component,OnInit } from '@angular/core'; import { FormGroup,FormArray,FormBuilder,Validators } from "@angular/forms" @Component({   selector: 'my-app',   templateUrl: './app.component.html',   styleUrls: [ './app.component.css' ] }) export class AppComponent implements OnInit  {   jobForm:FormGroup   constructor(private jobfb:FormBuilder){}    ngOnInit(){     this.jobForm = this.jobfb.group({       hobbies:this.jobfb.array([         this.createHobbyFormGroup()       ])     })   }    addHobby(){     let hobbies = this.jobForm.controls.hobbies as FormArray;     hobbies.push(this.createHobbyFormGroup());   }        createHobbyFormGroup(){     return this.jobfb.group({       hobbyName:['',Validators.required]     });   }  }

below is my Html code

<button (click)="addHobby()">Add Hobby</button> <table>   <tr [formGroup]="hobbyFG" *ngFor="let hobbyFG of jobForm.controls.hobbies.controls;">     <input formControlName="hobbyName"/>   </tr> </table> <button [disabled]="!jobForm.valid">Submit</button>

whenever user click on add button, at that time new FormGroup will be added in the FormArray.

I am not able to figure out how can I validate the hobby name, which should be unique?

Please guide.