In my ViewModel I have the following method that returns me the css class depending on `pState`:

```
function MyViewModel()
{
    var self = this;

    self.GetClass = function(pState) 
    {
        var lCssClass;

        switch(pState)
        {
            case "warning": 
                lCssClass = 'bg-yellow';
                break;
            case "red":
                lCssClass = 'font-red';
                break;
            default:
                lCssClass = 'font-default';
                break;
        }

        return lCssClass;
    };
}

```

I want to add the class in my view:

```
<span class="list-item" data-bind="attr : { class : $root.GetClass('warning')}">This is a warning.</span>

```

My problem: the existing class `list-item` will be overridden.

Here is a fiddle: <http://jsfiddle.net/d8L6v9h7/>