let caoButton = document.querySelector('.js-cao-2');

caoButton.addEventListener('click',firstFunctionality);

function firstFunctionality(){
  caoButton.removeEventListener('click', firstFunctionality)
  caoButton.addEventListener('click',secondFunctionality);
  //do stuff here
}

function secondFunctionality(){
  caoButton.removeEventListener('click', secondFunctionality)
  caoButton.addEventListener('click', firstFunctionality);
  //do something different here
}