p3.component.ts

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

@Component({
  selector: 'app-p3',
  templateUrl: './p3.component.html',
  styleUrls: ['./p3.component.css']
})
export class P3Component implements OnInit {

  widthLength = '1024';
  heightLength = '768';
  imageUrl = null;

  ngOnInit() {
    this.showPic();
  }

  showPic() {
    if (this.widthLength !== null && this.heightLength !== null &&
      this.widthLength !== undefined && this.heightLength !== undefined) {
      this.imageUrl = 'https://lorempixel.com/' + this.widthLength + '/' + this.heightLength + '/';
    } else {
      alert('null');
    }
  }

  constructor() { }

}