Show thumbnail preview of image before upload

Is there any ruby way to show thumbnail preview of image before upload?

Using below javascript, I can achieve this

     window.URL = window.URL || window.webkitURL;

  var fileElem = document.getElementById("fileElem");

  function handleFiles(files) {
    var img = document.getElementById("image-preview");

    if (!files.length) {
      img.src = "/img/default-profile-image.png";
    } else {
      img.src = window.URL.createObjectURL(files[0]);
      img.height = 60;
      img.onload = function(e) {


but I want to keep the thumbnail image in the case of validation fails.

Please help me....

Thanks in advance,


There can't be! Ruby needs you to have that image on the server to
generate a thumb of it, but before the upload it is not on the server.

What you try here, is not possible in PHP, whatever.NET or any other
kind of server-side-scripting-language.

But wait… Once, I stumbled upon a project, that is a ruby-interpreter
implemented in JavaScript, but can't remember its name. With that it
would be possible to generate the preview, but not to save it