PageMethods is not defined

 [WebMethod]
protected void getLecturesOnEdit()
        {
            int ss = Convert.ToInt32(txtEditlecturerNameHiden.Value);

            List<bl_User> lecturerList = new List<bl_User>();
            bl_User lecturer = new bl_User();
            lecturerList = lecturer.getLecturesList(ss);
            cboEditLecturer.DataSource = lecturerList;
            cboEditLecturer.DataTextField = "fullName";
            cboEditLecturer.DataValueField = "userID";
            cboEditLecturer.DataBind();}

function onEditModule() {
 

    PageMethods.getLecturesOnEdit();


   


}