Insert shortcode in post editor from javascript (Visual / HTML)

I was pulling my hair out on this one, but I might have figured it out.

Try this (with jQuery):

if( ! tinyMCE.activeEditor || tinyMCE.activeEditor.isHidden()) {
  jQuery('textarea#content').val("[SHORTCODE]test[/SHORTCODE] ");
} else {
  tinyMCE.execCommand('mceInsertRawHTML', false, "[SHORTCODE]test[/SHORTCODE] ");
}

Basically, you need to set the value of the textarea directly if the editor is hidden.