Changing root container mode property

I’m trying to allow the user to select if the root container in a view is in percent or fixed mode. I have this change script on a check box in the container:

    if currentValue.value:
        self.parent.props.mode='percent'
    else:
        self.parent.props.mode='fixed'

In the designer, it changes the mode as expected. However, when I save this and try to use it in the browser, the check box has no effect on how things are displayed. Why is this? Is there a better way to let users control the mode?