How To Access ASP.NET Web.config AppSettings On Client-Side Javascript
There are many ways by which you can access your ASP.NET web application web.config application settings through your client-side javascript code. The common thing between all of these ways is that to do so you for sure need to access the server-side. The most proper way I prefer is to load all your application settings in a batch the first time your page is loaded.
This article is a walkthrough which takes you from the early steps of writing the code up to its final form.