import { Pipe , PipeTransform } from "@angular/core" ; interface User { name ? : string ; email : string ; } @ Pipe ( { name : "userName" , } ) export class UserNamePipe implements PipeTransform { transform ( user ? ) { if ( user == null ) { return null ; } return user . name == null || user . name . trim ( ) === "" ? user . email : user . name ; } }