Access property from component in provider in angular2 - oop

Question

So I'm new to OOP and trying out ionic 2 with angular 2 with typescript.
Say I have an input in the home.html file that is coupled to username in home.ts like this:
export class HomePage {
public username: string;
public newusername: string;
...
constructor(public users: UserService) {
...
Now I want a service (userService.ts) to take username from the input or home.ts and modify it and store the result as newusername.
Do I have to make a constructor in the service/provider like in Homepage which instantiates a new object of home though I already made an object of this in home.ts?
I imported HomePage in userServices but I cant access newusername because I didnt make an object of it.

Answer 1

I don't know what exactly you want but take a look at this if its good for you. (I'd use newusername in service itself)
NOTE: its has nothing to do with Ionic2 as I don't know Ionic2.
Working demo: https://plnkr.co/edit/03oXUTZYwRRo8PTfDFlA?p=preview
import { Component } from '#angular/core';
import {service} from './service';
#Component({
selector: 'my-app',
template: `
New User : {{s.newusername}}<br>
<input type="text" [(ngModel)]="username">
<button (click)="click(username)">Add User</button>
`
})
export class AppComponent {
constructor(private s:service){
}
click(username){
this.s.addUserName(username);
console.log(this.s.newusername)
}
}
service.ts
import {Injectable} from '#angular/core';
#Injectable()
export class service{
newusername:string;
addUserName(str){
this.newusername=str;
}
}

Answer 2

You would need to call a service from code in the component, or pass the component to the service.
constructor(public users: UserService) {}
#Input() public username: string;
// called when an input was updated
ngOnChanges() {
this.newusername = this.users.convertUserName(this.username);
}
or
constructor(public users: UserService) {
users.component = this;
}
but this would still need some way to notify the service about changes to the input like in the above example.