Custom bindings for toggle Collapse Text

gistfile1.html

<a class="accordion-toggle" data-toggle="collapse" 
      data-parent="#accordion2" href="#collapseOne" 
      data-bind="toggleCollapseText: {openedText: '@GetText("AdvancedOptions") &#x25B2;', closedText: '@GetText("AdvancedOptions") &#x25bc;'}">
      @GetText("AdvancedOptions") &#x25B2;
  </a>

ko-bindingHandler-toggleCollapseText.js

(function($) {
    ko.bindingHandlers.toggleCollapseText = {
        init: function(element, valueAccesor){
            var opts = ko.utils.unwrapObservable(valueAccesor());
            $(element).on('click', function(){
                $(this).text(function(i, old){
                    return $.trim(old) == opts.closedText ? opts.openedText : opts.closedText;
                });
            });
        }
    };
})($);