panel/app/assets/javascripts/image_preview.js

$(document).on('turbolinks:load', function() {
  $('input[type=file]').on('change', function(event) {
    if (event.target.files.length == 0) return;

    var input = $(event.target);
    var preview = $(`#${input.data('preview')}`);

    preview.attr('src',
                 window.URL.createObjectURL(event.target.files[0]));
  });
});