This helper class adds Eval so that you can obtain the result of a JavaScript function. This functionality is not native to WatiN. Forked from: http://blog.ashmind.com/2007/09/05/evaluating-javascript-in-watin

WatiNHelper.cs

// Forked from: http://blog.ashmind.com/2007/09/05/evaluating-javascript-in-watin/
// This helper class adds Eval so that you can obtain the result of a JavaScript
// function. This functionality is not native to WatiN.

/*  
*  Usage: 
*  var browser = new IE();
*  var foo = browser.NativeDocument.Eval<bool>("isFoo()");
*/

public static class WatiNHelper
{
    public static T Eval<T>(this INativeDocument document, string code)
    {
        IExpando window = GetWindow(document);
        PropertyInfo property = GetOrCreateProperty(window, "__lastEvalResult");

        document.RunScript("window.__lastEvalResult = " + code + ";", "JavaScript");

        return (T)property.GetValue(window, null);
    }

    private static PropertyInfo GetOrCreateProperty(IExpando expando, string name)
    {
        PropertyInfo property = expando.GetProperty(name, BindingFlags.Instance);
        if (property == null)
        {
            property = expando.AddProperty(name);
        }

        return property;
    }

    private static IExpando GetWindow(INativeDocument document)
    {
        IEDocument ieDoc = document as IEDocument;
        IHTMLDocument2 htmlDoc = ieDoc.HtmlDocument;
        return htmlDoc.parentWindow as IExpando;
    }
}