Screen object contains the screen size of the currently selected device.
Note that these values change when you rotate a device between portrait and landscape modes.
# Results for an iPhone 8 in portrait orientation print Screen.width » 750 print Screen.height » 1334
With the Canvas device selected
Screen will contain the dimensions of the Preview Window (which is resizable).
You can also use
midY to get the horizontal or vertical center of the screen, just like with a layer.
print Screen.midX » 375 print Screen.midY » 667