Adapted from https://stackoverflow.com/a/14572970.

ScrollViewDepth.swift

extension NSScrollView {

  var documentSize: NSSize {
    set { documentView?.setFrameSize(newValue) }
    get { documentView?.frame.size ?? NSSize.zero }
  }

  var documentOffset: NSPoint {
    set { documentView?.scroll(newValue) }
    get { documentVisibleRect.origin }
  }

  var isScrolledToEnd: Bool {
    self.frame.height - (self.documentSize.height - self.documentOffset.y) == 0
  }
}