Get file size, image width and height before upload

Question

How can I get the file size, image height and width before upload to my website, with jQuery or JavaScript?

Answer 1

Multiple images upload with info data preview

Using HTML5 and the File API

Example using URL API

The images sources will be a URL representing the Blob object

const EL_browse  = document.getElementById('browse');
const EL_preview = document.getElementById('preview');

const readImage  = file => {
  if ( !(/^image\/(png|jpe?g|gif)$/).test(file.type) )
    return EL_preview.insertAdjacentHTML('beforeend', `Unsupported format ${file.type}: ${file.name}
`);

  const img = new Image();
  img.addEventListener('load', () => {
    EL_preview.appendChild(img);
    EL_preview.insertAdjacentHTML('beforeend', `
${file.name} ${img.width}×${img.height} ${file.type} ${Math.round(file.size/1024)}KB
`);
    window.URL.revokeObjectURL(img.src); // Free some memory
  });
  img.src = window.URL.createObjectURL(file);
}

EL_browse.addEventListener('change', ev => {
  EL_preview.innerHTML = ''; // Remove old images and data
  const files = ev.target.files;
  if (!files || !files[0]) return alert('File upload not supported');
  [...files].forEach( readImage );
});

#preview img { max-height: 100px; }

Example using FileReader API

In case you need images sources as long Base64 encoded data strings

const EL_browse  = document.getElementById('browse');
const EL_preview = document.getElementById('preview');

const readImage = file => {
  if ( !(/^image\/(png|jpe?g|gif)$/).test(file.type) )
    return EL_preview.insertAdjacentHTML('beforeend', `
Unsupported format ${file.type}: ${file.name}
`);

  const reader = new FileReader();
  reader.addEventListener('load', () => {
    const img  = new Image();
    img.addEventListener('load', () => {
      EL_preview.appendChild(img);
      EL_preview.insertAdjacentHTML('beforeend', `
${file.name} ${img.width}×${img.height} ${file.type} ${Math.round(file.size/1024)}KB
`);
    });
    img.src = reader.result;
  });
  reader.readAsDataURL(file);  
};

EL_browse.addEventListener('change', ev => {
  EL_preview.innerHTML = ''; // Clear Preview
  const files = ev.target.files;
  if (!files || !files[0]) return alert('File upload not supported');
  [...files].forEach( readImage );
});

#preview img { max-height: 100px; }