def js_add_el_to_div(class_name_source, class_name_target):
    """
    Js function to append source element to the target one.
    """
    js = f"const el = document.getElementsByClassName('{class_name_target}')[0];"
    js += "if (el) "
    js += f"el.appendChild(document.getElementsByClassName('{class_name_source}')[0])"
    return js