Gio.FilenameCompleter.prototype.get_completion_suffix

function get_completion_suffix(initial_text: String): String {
    // Gjs wrapper for g_filename_completer_get_completion_suffix()
}

Obtains a completion for initial_text from completer.

initial_text: text to be completed.
Returns: a completed string, or null if no completion exists. This string is not owned by GIO, so remember to GLib.free it when finished.