I have the below javascript preventdefault issue.
I'm not very good at javascript, but this is what my code.
The `event.preventDefault` is not working, however if I replace to `alert("SOMETEXT")`, it is showing up the alert.

```
function changecartitemquantitykeydown(itemid,event) {
// Allow: backspace, delete, tab, escape, and enter
if ( event.keyCode == 46 || event.keyCode == 8 || event.keyCode == 9 || event.keyCode == 27 || event.keyCode == 13 || 
     // Allow: Ctrl+A
    (event.keyCode == 65 && event.ctrlKey === true) || 
     // Allow: home, end, left, right
    (event.keyCode >= 35 && event.keyCode <= 39)) {
         // let it happen, don't do anything
         return;
}
else {
    // Ensure that it is a number and stop the keypress
    if ((event.shiftKey || (event.keyCode < 48 || event.keyCode > 57) && (event.keyCode < 96 || event.keyCode > 105 )) || (this.value.length == 0 && event.keyCode == 48)) {
        event.preventDefault(); <===== This is not happening
    }   
}
}

```