1. @DomName('MouseEvent.getModifierState')
  2. @DocsEditable()
  3. @Experimental()
bool getModifierState(String keyArg)

Source 

@DomName('MouseEvent.getModifierState')
@DocsEditable()
@Experimental() // untriaged
bool getModifierState(String keyArg) => _blink.BlinkMouseEvent.instance
    .getModifierState_Callback_1_(this, keyArg);