How to clear text field automatically when enter minus value

`

<input type="number" id="qty">
<input type="button" onclick="add()" value="Add">

<script>
  function add(){
    qty = document.getElementById('qty').value
    if(qty>0){
        var tot = qty*25
        document.write(tot)
    
    }else{
        qty = ""
        alert("no")
    }
  }
</script>

‘qty=""’ is the correct way as mentioned on google. but not working for me.

>Solution :

Try

document.getElementById("qty").value = "";

and cast qty to number in your if

if(Number(qty) > 0)