         if @revision_num == @length-1 then @forward_button.addClass("disabled") else @forward_button.removeClass("disabled")
 
     render_slider: =>
+        if not @syncstring?
+            return
         @length = @syncstring.all_versions().length
         @revision_num = @length - 1
         if @ext != "" and require('./editor').file_associations[@ext]?.opts.mode?

        @set_doc(@goto_revision(@revision_num))

    resize_slider: =>
        new_len = @syncstring.all_versions().length
        if new_len == @length
            return

        @goto_revision()

    render_diff_slider: =>
        if not @syncstring?
            return
        @length = @syncstring.all_versions().length
        @revision_num = @length - 1
        # debounce actually setting the document content just a little
