Read web part properties with javascript

The scenario: You have a visual web part with one or more properties you need to read from some javascript code related to the web part.

One way to do this, is to add a hidden html input control (with runat=server set) to the user control.
In the code behind for the user control assign the value of the property to the input element like this:

        protected override void OnPreRender(EventArgs e)

        {

            base.OnPreRender(e);

            if (this.WebPart != null)

            {

                wsurl.Value = WebPart.ValidationWebServiceUrl;

            }

        }

In the code above "wsurl" is the id of my hidden html input control, and "ValidationWebServiceUrl" is the property on my web part.

Voila - now you can read the value of the input element containing the property value from javascript. :-)