<input type="button" id="buttonCountPlus" value="+">
<input type="button" id="buttonCountMinus" value="-">
<div id="buttonCountNumber"></div>

document.getElementById("buttonCountPlus").onclick = function() {
  let count = document.getElementById("buttonCountNumber").innerHTML;
  if(+count <= 3){
    document.getElementById("buttonCountNumber").innerHTML++;
  }
}

document.getElementById("buttonCountMinus").onclick = function() {
  let count = document.getElementById("buttonCountNumber").innerHTML;
  if(+count >= 2){
    document.getElementById("buttonCountNumber").innerHTML--;
  }
}