dev@1: import { Injectable } from '@angular/core';
dev@1: 
dev@1: @Injectable()
dev@1: export class MailService {
dev@1: 
dev@1:   messages = [
dev@1:     {id: 0, text: `You've got mail!`},
dev@1:     {id: 1, text: `No Mail!`},
dev@1:     {id: 2, text: `Spam!`}
dev@1:   ];
dev@1: 
dev@1:   constructor() { }
dev@1: 
dev@1:   update(id, text) {
dev@1:     this.messages = this.messages.map(message =>
dev@1:       message.id === id
dev@1:         ? {id, text}
dev@1:         : message
dev@1:     )
dev@1:   }
dev@1: 
dev@1: }