This is now managed officially here: https://github.com/codearachnid/knockout.extend

ko.extended.js

// This is now managed officially here: https://github.com/codearachnid/knockout.extend
// custom binding attrIf which will check the value of a specific observable boolean before add or not the attributes
ko.bindingHandlers.attrIf = {
    update: function (element, valueAccessor, allBindingsAccessor) {
        var h = ko.utils.unwrapObservable(valueAccessor());
        var ifShow = ko.utils.unwrapObservable(h._if);
        if (ifShow) {
            ko.bindingHandlers.attr.update(element, valueAccessor, allBindingsAccessor);
        } else {
            for (var k in h) {
                if (h.hasOwnProperty(k) && k.indexOf("_") !== 0) {
                    $(element).removeAttr(k);
                }
            }
        }
    }
};

// custom method to bulk shove items into an observableArray
ko.observableArray.fn.pushAll = function (valuesToPush) {
    var underlyingArray = this();
    this.valueWillMutate();
    ko.utils.arrayPushAll(underlyingArray, valuesToPush);
    this.valueHasMutated();
    return this;
};

//https://github.com/ivaynberg/select2/wiki/Knockout.js-Integration
ko.bindingHandlers.select2 = {
    init: function(element, valueAccessor) {
        $(element).select2(valueAccessor());

        ko.utils.domNodeDisposal.addDisposeCallback(element, function() {
            $(element).select2('destroy');
        });
    },
    update: function(element) {
        $(element).trigger('change');
    }
};