Gtk.Window.prototype.deiconify
function deiconify():void { // Gjs wrapper for gtk_window_deiconify() }
Asks to deiconify (i.e. unminimize) the specified window. Note that you shouldn't assume the window is definitely deiconified afterward, because other entities (e.g. the user or <link linkend="gtk-X11-arch">window manager</link>) could iconify it again before your code which assumes deiconification gets to run.
You can track iconification via the "window-state-event" signal on Gtk.Widget.