load-all-files.js

const [images, setImages] = useState([]);

function loadFileAsync(file) {
  const reader = new FileReader();
  return new Promise((resolve, reject) => {
      reader.onloadend = (e) => {
        resolve(e.target.result);
      };
      // TODO handle error
      reader.readAsDataURL(file); 
  });  
}

function handleChanges(e) {
  const {files} = e;
  if (files.length) {
     Promise.all(files.map((file) => loadFileAsync(file))).then((images) => setImages(images));
  }
}