The define_action_button method supports one more optional parameter condition. This parameter is used to hide/show the button based on some condition. The value of this parameter is the function that returns the boolean. Based on the returned value, the Point of Sale system will hide or show the button. Take the look at the following example for more information:

screens.define_action_button({
    'name': 'reprint',
    'widget': ReprintButton,
    'condition': function(){
        return this.pos.config.print_via_proxy;
    }
});