simple-promise.js

const loadPhoto = photo_url =>
  new Promise(resolve => {
    const img = new Image();

    img.addEventListener('load', () => { 
      resolve(img);
    }, false);

    img.addEventListener('error', () => {
      const rejection = Promise.reject(new Error('Image could not be loaded.'));
      resolve(rejection);
    }, false);
    
    img.src = photo_url;
  });