         @view_doc?.hide()
 
     load_full_history: (cb) =>
+        if not @syncstring?
+            return
         n = @syncstring.all_versions().length
         @syncstring.load_full_history (err) =>
             if err

        if @revision_num == @length-1 then @forward_button.addClass("disabled") else @forward_button.removeClass("disabled")

    render_slider: =>
        @length = @syncstring.all_versions().length
        @revision_num = @length - 1
        if @ext != "" and require('./editor').file_associations[@ext]?.opts.mode?

            return
        if not num1?
            num1 = @revision_num1 ? Math.max(0, Math.floor(num2/2))
        versions = @syncstring?.all_versions()
        if not versions?
            # not yet initialized or closing
            return
        time1 = versions[num1]
        if not time1?
