CSS Class binding for Knockout.js

CssClassBinding.js

//
// Observable CSS Class Binding
//
// See Fiddle for usage: http://jsfiddle.net/kamranayub/3ahUA/
//
ko.bindingHandlers['class'] = {
    update: function (element, valueAccessor) {
        var currentValue = ko.utils.unwrapObservable(valueAccessor()),
            prevValue = element['__ko__previousClassValue__'],
            
            // Handles updating adding/removing classes
            addOrRemoveClasses = function (singleValueOrArray, shouldHaveClass) {
                if (Object.prototype.toString.call(singleValueOrArray) === '[object Array]') {          
                    ko.utils.arrayForEach(singleValueOrArray, function (cssClass) {
                      var value = ko.utils.unwrapObservable(cssClass);
                      ko.utils.toggleDomNodeCssClass(element, value, shouldHaveClass);
                    });
                } else if (singleValueOrArray) {
                    ko.utils.toggleDomNodeCssClass(element, singleValueOrArray, shouldHaveClass);
                }
            };
        
        // Remove old value(s) (preserves any existing CSS classes)
        addOrRemoveClasses(prevValue, false);
        
        // Set new value(s)
        addOrRemoveClasses(currentValue, true);
        
        // Store a copy of the current value
        element['__ko__previousClassValue__'] = currentValue.concat();
    }
};