Preload images in pure Javascript

preload.js

const preload = src => new Promise(function(resolve, reject) {
  const img = new Image();
  img.onload = function() {
    resolve(img);
  }
  img.onerror = reject;
  img.src = src;
});

const preloadAll = sources =>
  Promise.all(
    sources.map(
      preload));

const sources = [
  'https://i.picsum.photos/id/1000/5626/3635.jpg',
  'https://i.picsum.photos/id/10/2500/1667.jpg',
  'https://homepages.cae.wisc.edu/~ece533/images/cat.png',
  'https://homepages.cae.wisc.edu/~ece533/images/airplane.png'];

preloadAll(sources)
  .then(images => console.log('Preloaded all', images))
  .catch(err => console.error('Failed', err));