how to call web method in java script

<script>
 function DonwnlodFile(PLocMapFilePath) {

            $.ajax({
                type: "POST",
                url: '<%=ResolveUrl("~/Services/Property/Property.asmx/download") %>',
                data: "{}",
                contentType: "application/json; charset=utf-8",
                success: function (res) {
                    alert("Sdsdasad");
                    alert(res);
                    //  console.log("donwloaded");
                }
            });
        }

<script>

In services

    public void download()

    {

        string filename = "test.txt";

        string path = "C:\\Users\\JITENDRA\\Desktop\\test.txt";

        byte[] ls1 = DownloadFile(path);

        HttpResponse response = Context.Response;

        response.Clear();

        response.BufferOutput = true;

        response.ContentType = "application/octet-stream";

        response.ContentEncoding = Encoding.UTF8;

        response.AppendHeader("content-disposition", "attachment; filename=" + filename);

        response.BinaryWrite(ls1);

        response.Flush();

        response.Close();

    }

    [WebMethod()]

    public byte[] DownloadFile(string FName)

    {

        System.IO.FileStream fs1 = null;

        fs1 = System.IO.File.Open(FName, FileMode.Open, FileAccess.Read);

        byte[] b1 = new byte[fs1.Length];

        fs1.Read(b1, 0, (int)fs1.Length);

        fs1.Close();

        return b1;

    }