     @_inprogress = yes
 
     {JSEditor, PreviewPane} = @workspace.activePanel.panesByName
-    extension = JSEditor.getData()?.getExtension() or 'coffee'
+    editorData = JSEditor.getData()
+    extension = if editorData then editorData.getExtension() else 'coffee'
 
     if extension not in ['js', 'coffee']
       @_inprogress = no
-      log "Not supported!"
-      PreviewPane.container.destroySubViews()
+      pc = PreviewPane.container
+      pc.destroySubViews()
+      pc.addSubView new ErrorPaneWidget {},
+        error     :
+          name    : "Preview not supported"
+          message : "You can only preview .coffee and .js files."
       return
 
     @compiler (coffee)=>

              name              : "finder"
              editor            : "JSEditor"
              handleFileOpen    : (file, content) =>
                # log file, content
                panes = @workspace.activePanel.panesByName
                switch FSItem.getFileExtension file.path
                  when 'css', 'styl'
                  then panes.CSSEditor.openFile file, content
                  else panes.JSEditor.openFile file, content
            }
            {
              type              : "split"


  pistachio:->
    {error} = @getData()
    line    = if error.location then "at line: #{error.location.last_line+1}" else ""
    stack   = if error.stack? then """
      <div class='stack'>
        <h2>Full Stack</h2>
        <pre>#{error.stack}</pre>
      </div>
    """ else ""

    """
      {h1{#(error.name)}}
      <pre>#{error.message} #{line}</pre>
      #{stack}
    """

  click:-> @setClass 'in'