Creates a primitive rectangle for the current selection. Useful when adding background for text boxes.

Create Background.jsfl

// by @blvz

var padding = 10
,   radius  = 10;

(function(doc) {
  var bounds, rect, newRect, fill, stroke
  , tml = doc.getTimeline()
  , sel = doc.selection.concat()
  , rs  = sel.filter(function(e) { return e.elementType == 'shape'
                                       && e.isRectangleObject })

  sel = sel.filter(function(e) { return e !== rect })

  if (!sel.length) return

  rect = rs[0]
  if (rect) rect.selected = false

  bounds = doc.getSelectionRect()
  bounds.left   -= padding
  bounds.top    -= padding
  bounds.right  += padding
  bounds.bottom += padding

  doc.selectNone()
  if (rect) rect.selected = true, fill = doc.getCustomFill(), stroke = doc.getCustomStroke()
  doc.addNewPrimitiveRectangle(bounds, 0)
  doc.selectNone()

  newRect = tml.layers[tml.currentLayer].frames[tml.currentFrame].elements.concat().pop()
  newRect.selected = true
  doc.setRectangleObjectProperty('lockFlag', true)
  doc.setRectangleObjectProperty('topLeftRadius', radius)
  if (rect) doc.setCustomFill(fill), doc.setCustomStroke(stroke)
  doc.selectNone()

  if (rect) rect.selected = true, doc.deleteSelection()

  sel.forEach(function(e) { e.selected = true })
  doc.clipCut()
  doc.clipPaste(true)

  newRect.selected = true
})(fl.getDocumentDOM())