I found that ResolveClientUrl() works as expected when JavaScript is embedded in ASPX page, however it doesn't resolve anything when external script is referenced in ASPX like this:
<script src="../Javascript/sessionManagement.js" type="text/javascript"></script>
Is there a way to make ResolveClientUrl() work in external JS files? I was expected that it would because this file IS included in ASPX page but this is not the case.
I found a rather ugly workaround - to include external JS file in ASPX page like this:
<script type="text/javascript" language="jscript">
<!--#include file="../Javascript/sessionManagement.js"-->
</script>
It works (ResolveClientUrl() actually resolves path) but I've never seen external JS files referenced like that and am not sure this is the way to go.
.aspxpages, you can't run inline C# or VB code on them. Instead, run it directly on the .aspx page and then access that variable from your JS, or pass it through a function.