test.component.ts

import {Component, OnInit, Input} from '@angular/core';

@Component({
  selector: 'app-test',
  templateUrl: './test.component.html',
  styleUrls: ['./test.component.scss']
})
export class TestComponent implements OnInit {

  @Input() counter: number;
  constructor() {
    this.counter = 0;
  }

  ngOnInit() {
  }

  addOne() {
    this.counter++;
  }

}