If we need to bind complex JS objects to select HTML element in knockout with optgroups then the following jsfiddle has great sample
http://jsfiddle.net/rniemeyer/aCS7D/
so the HTML binding looks like:
<select data-bind="foreach: groups, value: selectedOption">
<optgroup data-bind="attr: {label: label}, foreach: children">
<option data-bind="text: label, option: $data"></option>
</optgroup>
</select>
<hr />
<div data-bind="text: specialProperty"></div>
and js code looks like:
ko.bindingHandlers.option = {
update: function(element, valueAccessor) {
var value = ko.utils.unwrapObservable(valueAccessor());
ko.selectExtensions.writeValue(element, value);
}
};
function Group(label, children) {
this.label = ko.observable(label);
this.children = ko.observableArray(children);
}
function Option(label, property) {
this.label = ko.observable(label);
this.someOtherProperty = ko.observable(property);
}
var ViewModel = function() {
this.groups = ko.observableArray([
new Group("Group 1", [
new Option("Option 1", "A"),
new Option("Option 2", "B"),
new Option("Option 3", "C")
]),
new Group("Group 2", [
new Option("Option 4", "D"),
new Option("Option 5", "E"),
new Option("Option 6", "F")
])
]);
this.selectedOption = ko.observable();
this.specialProperty = ko.computed(function(){
var selected = this.selectedOption();
return selected ? selected.someOtherProperty() : 'unknown';
}, this);
};
ko.applyBindings(new ViewModel());
http://jsfiddle.net/rniemeyer/aCS7D/
so the HTML binding looks like:
<select data-bind="foreach: groups, value: selectedOption">
<optgroup data-bind="attr: {label: label}, foreach: children">
<option data-bind="text: label, option: $data"></option>
</optgroup>
</select>
<hr />
<div data-bind="text: specialProperty"></div>
and js code looks like:
ko.bindingHandlers.option = {
update: function(element, valueAccessor) {
var value = ko.utils.unwrapObservable(valueAccessor());
ko.selectExtensions.writeValue(element, value);
}
};
function Group(label, children) {
this.label = ko.observable(label);
this.children = ko.observableArray(children);
}
function Option(label, property) {
this.label = ko.observable(label);
this.someOtherProperty = ko.observable(property);
}
var ViewModel = function() {
this.groups = ko.observableArray([
new Group("Group 1", [
new Option("Option 1", "A"),
new Option("Option 2", "B"),
new Option("Option 3", "C")
]),
new Group("Group 2", [
new Option("Option 4", "D"),
new Option("Option 5", "E"),
new Option("Option 6", "F")
])
]);
this.selectedOption = ko.observable();
this.specialProperty = ko.computed(function(){
var selected = this.selectedOption();
return selected ? selected.someOtherProperty() : 'unknown';
}, this);
};
ko.applyBindings(new ViewModel());