Can't get input value from contoller

I update input with id='total' with event onchange. When I fill quantity input, the input total is updated with correct value but when i try to get the value from controller, it returns null. Any idea? Thanks

This is the code:

                                            <div class="form-group" >
                                                <input type="text" name="quantity" class="form-control" id="quantity" onchange="updateInput(this.value)"  >
                                            </div>
                                        </td>

                                        <td align="center">
                                            <div class="form-group ">

                                                <input type="text" class="form-control" id="total" name="total" value="" disabled >
                                            </div>
                                        </td>

And this is function onchange

function updateInput(x)
                        {

                            var price=parseFloat(document.getElementById('price').value);
                           document.getElementById('total').value=parseFloat(x)*price;


                        }

via Chebli Mohamed