Question

How do you get an ASP.NET application relative URL from JavaScript?

Answer 1

You could always generate a set of constants for paths that you will be using in a way which Javascript can see. ex:

<script type="text/javascript">
    var Paths = {};
    var Paths.Images = '<%= ...MapPath("~/images") %>';
    var Paths.Scripts = '<%= ...MapPath("~/scripts") %>';
</script>

Of course, you can adapt this to your app’s needs. For example, it might not be a bad idea to stick the initial declaration of Paths in a common js file, and have a method in your master page to add paths you will definitely need on each page. Subpages can generate paths as needed, possibly from a helper method of some sort that generalizes the whole process.

edit: I’ve been thinking about this some more. Here’s a possible implementation, completely untested and probably not exactly right:

public static string RegisterPathsForJavascript(IDictionary<string,string> paths)
{
    var pathConstants = "";
    foreach(var path in paths)
    {
        pathConstants += string.Format("Paths.{0} = '{1}';\n",
            path.Key,
            Server.MapPath(path.Value));
    }
    return pathConstants;
}

and in your page:

<script type="text/javascript">
    <%= RegisterPathsForJavascript(new Dictionary<string, string> {
            { "Images", "~/images" },
            { "Scripts", "~/scripts" }
        }) %>

    alert(Paths.Images);
</script>