move some javascript to view

app/assets/javascripts/application/learning_objects_builder.js

-// show preview image
-$(function() {
-    $('#thumbnail_btn').on('change', function(event) {
-        var files = event.target.files;
-        var image = files[0]
-        var reader = new FileReader();
-        reader.onload = function(file) {
-            var img = new Image();
-            console.log(file);
-            img.src = file.target.result;
-            $('#preview_image_target').html(img);
-        }
-        reader.readAsDataURL(image);
-        console.log(files);
-    });
-});
\ No newline at end of file

app/views/learning_objects/build/select_thumbnail.html.erb

@@ -33,23 +33,12 @@
 
         <% unless @learning_object.thumbnail.blank? %>
             <div>
-              <%= image_tag @learning_object.default_thumbnail.url %>
+              <%= image_tag @learning_object.default_thumbnail.url(:small) %>
               <i id="remove_thumbnail" class="fa fa-trash fa-1"></i></div>
-            <script>
-              $("#remove_thumbnail").click(function(){
-                if(confirm("Você tem certeza?")){
-                  $(this).parent().remove()
-                  $.ajax({
-                    url: "<%= remove_thumbnail_path(@learning_object) %>",
-                    method: 'POST'
-                  })
-                }
-              });
-            </script>
         <% end %>
 
         <%=  f.file_field :thumbnail, required: true, id: 'thumbnail_btn'  %>
-        
+
         <button type="submit" class="btn-submit btn btn-success btn-outline-rounded green">
           Enviar <i style="margin-left:10px;" class="fa fa-paper-plane"></i>
         </button>
@@ -63,4 +52,32 @@
     <% end %>
 <% end %>
 
-<!--  -->
\ No newline at end of file
+<!--  -->
+<script>
+    $("#remove_thumbnail").click(function(){
+        if(confirm("Você tem certeza?")){
+            $(this).parent().remove()
+            $.ajax({
+                url: "<%= remove_thumbnail_path(@learning_object) %>",
+                method: 'POST'
+            })
+        }
+    });
+
+    // show preview image
+    $(function() {
+        $('#thumbnail_btn').on('change', function(event) {
+            var files = event.target.files;
+            var image = files[0]
+            var reader = new FileReader();
+            reader.onload = function(file) {
+                var img = new Image();
+                console.log(file);
+                img.src = file.target.result;
+                $('#preview_image_target').html(img);
+            }
+            reader.readAsDataURL(image);
+            console.log(files);
+        });
+    });
+</script>
\ No newline at end of file