<div>
  <input type="number" id="n" value="0">
  <button commandfor="n" command="--add" value="-10">-10</button>
  <button commandfor="n" command="--add" value="-1">-1</button>
  <button commandfor="n" command="--add" value="1">+1</button>
  <button commandfor="n" command="--add" value="10">+10</button>
</div>

const input = document.querySelector("#n");
input.addEventListener("command", (e) => {
  if (e.command === "--add") {
    e.target.value = Number(e.target.value) + Number(e.source.value);
  }
});