Untitled

<div>
  <p>Apples: <span id="apples">10</span></p>
    <button onclick="decrease('apples')">-1</button>
    </div>

    <script>
    function decrease(id) {
          let el = document.getElementById(id);
            let num = parseInt(el.innerText);
              if (num > 0) el.innerText = num - 1;
    }
    </script>
    
    }