I'm not sure if this is a documentation issue or a feature request, however I cannot find a way to maximize a window using a kwin script. 

I am looking at the documentation here: https://techbase.kde.org/Development/Tutorials/KWin/Scripting/API_4.9

You can set window.fullScreen = true; to make the window fullscreen and window.minimized = true; to minimize the window and there's a window.maximizable property which stores whether the window can be maximized but there doesn't seem to be a way to maximize the window via a script.

I tried window.maximized = true; in case the documentation was just missing the maximized property, but the documentation seems correct, there doesn't appear to be a maximized property.