Handlebar helper not executing on input change

<select name="state">
   
       <option value= disabled=></option>
    
</select>

When user select an option i will add that option to matchedFilters array. Now i want the selected option to be disabled. so i wrote a helper for that.

export function isSelected(params) {
  let selected = params[0];
  let options = params[1];
  return options.indexOf(selected) >= 0;;
}

But this helper is executing only on load. i want that helper to execute every time matchedFilters change.