implemented autosave, save button is now hidden. there is a label to show the last save timestamp. Code is saved on browser close.

app/assets/javascripts/editor.js

@@ -11,6 +11,7 @@ $(function() {
   var FILENAME_URL_PLACEHOLDER = '{filename}';
   var SUCCESSFULL_PERCENTAGE = 90;
   var THEME = 'ace/theme/textmate';
+  var AUTOSAVE_INTERVAL = 15 * 1000;
 
   var editors = [];
   var active_file = undefined;
@@ -317,6 +318,23 @@ $(function() {
     $('button i.fa-spin').hide();
   };
 
+  var autosaveTimer;
+  var autosaveLabel = $("#autosave-label span");
+
+  var resetSaveTimer = function(){
+    clearTimeout(autosaveTimer);
+    autosaveTimer = setTimeout(autosave, AUTOSAVE_INTERVAL);
+  };
+
+  var autosave = function(){
+    var date = new Date();
+    autosaveLabel.parent().css("visibility", "visible");
+    autosaveLabel.text(date.getHours() + ':' + date.getMinutes() + ':' + date.getSeconds());
+    autosaveLabel.text(date.toLocaleTimeString());
+    autosaveTimer = null;
+    createSubmission($('#autosave'), null);
+  }
+
   var initializeEditors = function() {
     $('.editor').each(function(index, element) {
       var editor = ace.edit(element);
@@ -326,6 +344,12 @@ $(function() {
         });
       }
 
+
+      // listener for autosave
+      editor.getSession().on("change", function (deltaObject) {
+        resetSaveTimer();
+      });
+
       var document = editor.getSession().getDocument();
       // insert pre-existing code into editor. we have to use insertLines, otherwise the deltas are not properly added
       var file_id = $(element).data('file-id');
@@ -983,6 +1007,13 @@ $(function() {
         }
     }
 
+  $(window).on("beforeunload", function() {
+    if(autosaveTimer){
+      autosave();
+    }
+
+  })
+
   if ($('#editor').isPresent()) {
       if (isBrowserSupported()) {
           initializeCodePilot();

app/assets/stylesheets/editor.css.scss

@@ -31,7 +31,7 @@ button i.fa-spin {
 
 #editor-buttons {
   background-color: #008CBA;
-  margin-top: 1em;
+  margin-top: 0;
   width: 100%;
 
   button {
@@ -39,7 +39,7 @@ button i.fa-spin {
   }
 
   button, .btn-group {
-    width: 25%;
+    width: 33.33333%;
   }
 
   .btn-group {
@@ -80,3 +80,11 @@ button i.fa-spin {
 #results {
   display: none;
 }
+
+#autosave-label{
+  visibility: hidden;
+  height: 1.6em;
+  text-align:  right;
+  color: #777;
+  font-size: 0.8em;
+}