Using knockout js with jquery ui sliders

I'm trying to figure out if knockout js would work nicely for the following problem:

I have multiple sliders that I want to link to textboxes.

When the textbox is changed the corresponding slider must update to the new value and vice versa.

On changing the slider value or textbox a function needs to be called that uses the input from all textboxes to calculate a result.

I have my quick and dirty jQuery solution here.

Would it be easy to achieve the same result in a more elegant way using knockout js?

I guess I would need to create a custom binding handler like its done in jQuery UI datepicker change event not caught by KnockoutJS

Here is an example: http://jsfiddle.net/jearles/Dt7Ka/

I use a custom binding to integrate the jquery-ui slider and use Knockout to capture the inputs and calculate the net amount.

--

UI

<h2>Slider Demo</h2>

Savings: <input data-bind="value: savings, valueUpdate: 'afterkeydown'" />
<div style="margin: 10px" data-bind="slider: savings, sliderOptions: {min: 0, max: 100, range: 'min', step: 1}"></div>

Spent: <input data-bind="value: spent, valueUpdate: 'afterkeydown'" />
<div style="margin: 10px" data-bind="slider: spent, sliderOptions: {min: 0, max: 100, range: 'min', step: 1}"></div>

Net: <span data-bind="text: net"></span>

View Model

ko.bindingHandlers.slider = {
  init: function (element, valueAccessor, allBindingsAccessor) {
    var options = allBindingsAccessor().sliderOptions || {};
    $(element).slider(options);
    $(element).slider({
        "slide": function (event, ui) {
            var observable = valueAccessor();
            observable(ui.value);
        },
        "change": function (event, ui) {
            var observable = valueAccessor();
            observable(ui.value);
        }
    });
    ko.utils.domNodeDisposal.addDisposeCallback(element, function () {
        $(element).slider("destroy");
    });
  },
  update: function (element, valueAccessor) {
    var value = ko.unwrap(valueAccessor());
    if (isNaN(value)) {
        value = 0;
    }
    $(element).slider("value", value);
  }
};

var ViewModel = function() {
    var self = this;

    self.savings = ko.observable(10);
    self.spent = ko.observable(5);
    self.net = ko.computed(function() {
        return self.savings() - self.spent();
    });
}

ko.applyBindings(new ViewModel());

I know it's some days ago but I made a few adjustments to John Earles code:

ko.bindingHandlers.slider = {
init: function (element, valueAccessor, allBindingsAccessor) {
    var options = allBindingsAccessor().sliderOptions || {};
    $(element).slider(options);
    ko.utils.registerEventHandler(element, "slidechange", function (event, ui) {
        var observable = valueAccessor();
        observable(ui.value);
    });
    ko.utils.domNodeDisposal.addDisposeCallback(element, function () {
        $(element).slider("destroy");
    });
    ko.utils.registerEventHandler(element, "slide", function (event, ui) {
        var observable = valueAccessor();
        observable(ui.value);
    });
},
update: function (element, valueAccessor, allBindingsAccessor) {
    var value = ko.utils.unwrapObservable(valueAccessor());
    if (isNaN(value)) value = 0;
    $(element).slider("option", allBindingsAccessor().sliderOptions);
    $(element).slider("value", value);
}
};

The reason for this is that if you use options that change (fx another observable) then it won't affect the slider even if you wanted it to do so.

@John Earles and @Michael Kire Hansen: thanks for your wonderful solutions!

I used the advanced code from Michael Kire Hansen. I tied the "max:" option of the slider to a ko.observable and it turned out that the slider does not correctly update the value in this case. Example: Lets say the slider is at value 25 of max 25 und you change the max value to 100, the slider stays at the most right position, indicating that it is at the max value (but value is still 25, not 100). As soon as you slide one point to the left, you get the value updated to 99.

Solution: in the "update:" part just switch the last two lines to:

$(element).slider("option", allBindingsAccessor().sliderOptions);
$(element).slider("value", value);

This changes the options first, then the value and it works like a charm.