ใน javascript จะหา path ที่แท้จริงอย่างไรครับถ้าไม่ใส่ แบบ fullpath

Imports Microsoft.VisualBasic
Imports System.Data
Imports System.Data.SqlClient
Imports System.Text
Imports System.Collections
Imports System.Runtime.CompilerServices

Imports System.Web
Imports System.Web.UI
Imports System.Web.UI.WebControls

'Imports General
'Imports General.Convertor

Namespace System.Web.UI.Extensions
    Public Module PageExtension

#Region "Utility Section"

        ''' <summary>
        ''' Trace path from page for any javascript reference location
        ''' </summary>
        ''' <param name="Am"></param>
        ''' <param name="argPathFileLocation"></param>
        ''' <returns></returns>
        ''' <remarks></remarks>
        <Extension()> _
        Public Function TraceIncludeBasePath(ByVal Am As Page, ByVal argPathFileLocation As String) As String
            Dim strRet As String = argPathFileLocation
            Dim CurrentURLStr As String = Am.Server.MapPath(Am.Request.ServerVariables("URL"))
            Dim ScriptURL As String = Am.Server.MapPath(argPathFileLocation)
            Dim tempStr As String = String.Empty
            Dim founded As Boolean = False

            For i As Integer = 1 To ScriptURL.Length - 1
                tempStr = ScriptURL.Substring(0, i)
                If (Not tempStr.Equals(CurrentURLStr.Substring(0, i))) Then
                    founded = True
                    CurrentURLStr = CurrentURLStr.Substring(i - 1)
                    ScriptURL = ScriptURL.Substring(i - 1)
                    Exit For
                End If
            Next

            If (Not founded) Then Return String.Empty
            'After pass mappath path separator will be "\"
            Dim ixStr As String() = CurrentURLStr.Split(New Char() {"\"c}, StringSplitOptions.RemoveEmptyEntries)
            Dim totalTrace As Integer = ixStr.Length - 1

            'Replace to valid path separator
            strRet = ScriptURL.Replace("\"c, "/"c)
            For i As Integer = 0 To totalTrace - 1
                strRet = "../" + strRet
            Next

            Return strRet.ToUpper()
        End Function

        ''' <summary>
        ''' Adding any script file to page suggest to use when uses sub directory for any page
        ''' </summary>
        ''' <param name="Am"></param>
        ''' <param name="argScriptFileLocation"></param>
        ''' <remarks></remarks>
        <Extension()> _
        Public Sub HeaderAddNewScriptFile(ByVal Am As Page, ByVal argScriptFileLocation As String)
            Dim newScriptParser As New HtmlGenericControl("script")
            newScriptParser.Attributes.Add("src", Am.TraceIncludeBasePath(argScriptFileLocation))
            newScriptParser.Attributes.Add("type", "text/javascript")

            Am.Header.Controls.Add(New LiteralControl(vbTab))
            Am.Header.Controls.Add(newScriptParser)
            Am.Header.Controls.Add(New LiteralControl(Environment.NewLine))

        End Sub
    End Module
End Namespace

....
Imports System.Web.UI.Extensions

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        
        Me.HeaderAddNewScriptFile("~/Scripts/jquery-1.4.2.min.js")
        Me.HeaderAddNewScriptFile("~/Scripts/jquery-ui-1.8.1.custom.min.js")
        
        If (Not Page.IsPostBack) Then
  
        End If

    End Sub

Dim sb As New StringBuilder
sb.Append("<script type='text/javascript' language='javascript'>")
sb.Append("alert('usernameหรือpasswordไม่ถูกต้อง');")
sb.Append("document.location ='login.aspx';")
sb.Append("</script>")
Page.ClientScript.RegisterStartupScript(Page.GetType, "RedirectScript", sb.ToString)