You can currently disable resizing of the game window when exporting with NW.js on Construct 3. You can both dynamically enable/disable window resizing during runtime with the NW.js plugin, as well as disable it from the start of runtime by ticking the "Resizable window" export option for NW.js exports. Currently, the user has no visual way of telling whether the game window is resizable or not without attempting to drag the borders of the window, as the maximize button still appears to be usable.

I suggest that there should be an option to disable or hide the maximize button to prevent this issue.