knockout binding to disable and clear an element with value binding

disableClear.js

ko.bindingHandlers.disableClear = {
    update: function (element, valueAccessor, allBindingsAccessor) {
        var value = !ko.utils.unwrapObservable(valueAccessor());
        if (value && element.disabled)
            element.removeAttribute("disabled");
        else if ((!value) && (!element.disabled)) {
            //If there is a value binding, that's what we want to clear
            var valueBinding = allBindingsAccessor().value;
            if ( typeof(valueBinding) === 'function') {
                valueBinding('');
            }
            element.disabled = true;
        }
    }
};