Show username (String) using "Alert"

Hello! I have a probem because in my function doAlert() I would like show the username using “alert”, so… I need convert it to string for that. Somebody know how can I solve it?
Thanks in advance.

Best regards.

import {Component} from “@angular/core”;
import {NavController , Alert} from ‘ionic-angular’;
import {Principal} from ‘…/principal/principal’;
import { FORM_DIRECTIVES, FormBuilder, ControlGroup, Validators, AbstractControl } from ‘@angular/common’;
import {CustomValidators} from ‘…/validators/CustomValidators’;

templateUrl: ‘build/pages/home/home.html’,
directives: [FORM_DIRECTIVES]
export class HomePage {

authForm: ControlGroup;
username: AbstractControl;
password: AbstractControl;

constructor(private navController: NavController , private fb: FormBuilder) {

    this.authForm ={  
        'username': ['', Validators.compose([Validators.required, Validators.minLength(4), CustomValidators.checkFirstCharacterValidator])],
        'password': ['', Validators.compose([Validators.required, Validators.minLength(4), CustomValidators.checkFirstCharacterValidator])]

    this.username = this.authForm.controls['username'];     
    this.password = this.authForm.controls['password'];  

onSubmit(value: string): void { 
    if(this.authForm.valid) {
        console.log('Submitted value: ', value);


doAlert() {
        let alert = Alert.create({
            title: 'New Friend!',
            subTitle: this.username,
            buttons: ['OK']