Beginner struggling with creating plugins

   // Apply the given function to all chords/rests in selection
   // or, if nothing is selected, in the entire score
   function applyToChordsAndRestsInSelection(func) {
      var cursor = curScore.newCursor()
      cursor.rewind(Cursor.SELECTION_START)
      var startStaff
      var endStaff
      var endTick
      var fullScore = false
      if (!cursor.segment) { // no selection
         fullScore = true
         startStaff = 0 // start with 1st staff
         endStaff = curScore.nstaves - 1 // and end with last
         }
      else {
         startStaff = cursor.staffIdx
         cursor.rewind(Cursor.SELECTION_END)
         if (cursor.tick === 0) {
            // this happens when the selection includes
            // the last measure of the score.
            // rewind(Cursor.SELECTION_END)) goes behind the last segment
            // (where there's none) and sets tick=0
            endTick = curScore.lastSegment.tick + 1
            }
         else
            endTick = cursor.tick
         endStaff = cursor.staffIdx
         }
      console.log(startStaff + " - " + endStaff + " - " + endTick)
      curScore.startCmd()
      for (var staff = startStaff; staff <= endStaff; staff++) {
         for (var voice = 0; voice < 4; voice++) {
            cursor.rewind(Cursor.SELECTION_START) // sets voice to 0
            cursor.voice = voice //voice has to be set after goTo
            cursor.staffIdx = staff
 
            if (fullScore)
               cursor.rewind(Cursor.SCORE_START) // if no selection, beginning of score
 
            while (cursor.segment && (fullScore || cursor.tick < endTick)) {
               if (cursor.element) {
                  if (cursor.element.type === Element.REST)
                     func(cursor.element, voice)
                  else if (cursor.element.type === Element.CHORD) {
                     func(cursor.element, voice)
                     var graceChords = cursor.element.graceNotes;
                     for (var i = 0; i < graceChords.length; i++) {
                        // iterate through all grace chords
                        func(graceChords[i], voice)
                        var gnotes = graceChords[i].notes
                        for (var j = 0; j < gnotes.length; j++)
                           func(gnotes[j], voice)
                        }
                     var notes = cursor.element.notes
                     for (var k = 0; k < notes.length; k++) {
                        var note = notes[k]
                        func(note, voice)
                        }
                     } // end if CHORD
                  } // end if element
               cursor.next()
               } // end while cursor
            } // end for loop
         } // end for loop
      curScore.endCmd()
      }