Update the scroll position when 'fetch more messages' is complete

FREEBIE

js/views/conversation_view.js

@@ -156,7 +156,7 @@
             'focus .send-message': 'focusBottomBar',
             'change .file-input': 'toggleMicrophone',
             'blur .send-message': 'unfocusBottomBar',
-            'loadMore .message-list': 'fetchMessages',
+            'loadMore .message-list': 'loadMoreMessages',
             'newOffscreenMessage .message-list': 'addScrollDownButtonWithCount',
             'atBottom .message-list': 'hideScrollDownButton',
             'farFromBottom .message-list': 'addScrollDownButton',
@@ -312,6 +312,27 @@
             this.$messageField.focus();
         },
 
+        loadMoreMessages: function() {
+            if (this.inProgressFetch) {
+                return;
+            }
+
+            this.view.measureScrollPosition();
+            var startingHeight = this.view.scrollHeight;
+
+            this.fetchMessages().then(function() {
+                // We delay this work to let scrolling/layout settle down first
+                setTimeout(function() {
+                    this.view.measureScrollPosition();
+                    var endingHeight = this.view.scrollHeight;
+                    var delta = endingHeight - startingHeight;
+
+                    var newScrollPosition = this.view.scrollPosition + delta - this.view.
+                    this.view.$el.scrollTop(newScrollPosition);
+                }.bind(this), 1);
+            }.bind(this));
+        },
+
         fetchMessages: function() {
             console.log('fetchMessages');
             this.$('.bar-container').show();