ko.bindingHandlers.toggleSlide= {
    init: function(element, valueAccessor) {
        // Initially set the element to be instantly visible/hidden depending on the value
        var value = valueAccessor();
        $(element).toggleSlide(ko.unwrap(value)); // Use "unwrapObservable" so we can handle values that may or may not be observable
    },
    update: function(element, valueAccessor) {
        // Whenever the value subsequently changes, slowly fade the element in or out
        var value = valueAccessor();
        ko.unwrap(value) ? $(element).slideDown('fast') : $(element).slideUp('fast');
    }
};

////////////////////////////////////////

then on my button I have

click: filteredPageChoices

//////////////////////////////////////

then on the slide down element

toggleSlide: filteredPageChoices