text: /**
   * Universidad de La Laguna
   * Escuela Superior de Ingeniería y Tecnología
   * Grado en Ingeniería Informática
   * Programación de Aplicaciones Interactivas
   *
   * @author F. de Sande
   * @since 24.apr.2020
   * @desc Tic Tac Toe Example. Step 1
   */
  
  'use strict';
  
  const changeToX = function(event) {
    const X_IMAGE_URL = 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/1083533/x.png';
    const O_IMAGE_URL = 'https://s3-us-west-2.amazonaws.com/s.cdpn.io/1083533/circle.png';
    const container = event.currentTarget;
    const image = document.createElement('img');
    image.src = X_IMAGE_URL;
    container.appendChild(image);    // We add the image child to the div X-clicked element
    container.removeEventListener('click', changeToX);
  }
  
  const main = function() {
    const boxes = document.querySelectorAll('#grid div');
    for (const box of boxes) {
      box.addEventListener('click', changeToX);
    }
  }
  
  main();
  