Window.js has a simple console that is similar to the Javascript console in the Chrome devtools, and allows experimenting quickly with Javascript code and the Window.js APIs.

Keyboard shortcuts

These shortcuts work in the main window and the console window.

Escape Closes the main window.
F1 Opens the console for the current window.
F2 Overlays FPS and memory usage stats in the main window.
F3 Continuously logs frame times to the console. See details below.
F4 Overlays console logs in the main window.
F5 Reloads the initial module and refreshes the main window.
F6 Keeps the window always on top.
F8 Saves a screenshot named ScreenshotN.png to the current directory.

These shortcuts work in the console window only.

Escape Closes the console window.
Ctrl+r Reloads the initial module and refreshes the main window.
Ctrl+q Closes the main window.
Ctrl+c Copies the current input line to the clipboard.
Ctrl+v Pastes the current clipboard to the input line.


Javascript code can be written and submitted via the console. It gets executed in the context of the main window.

For example, starting with an empty window:


The console can be opened by pressing F1. Then typing this code in the console updates the title of the main window:

window.title = 'Hello world!'

Frame times

If enabled with F3 or by setting window.debug.profileFrameTimes, then a log line will be printed after each frame is finished. Example:

Input 0.141 GC 0.001 JS 0.003 RAF 0.200 Swap 7.749 Total frame 8.345 FPS 119.826

Elapsed times in milliseconds.

Input Time processing input events from the operating system. This does not include time in Javascript event listeners, except for resize events.
GC Time waiting for the Javascript lock used by the garbage collector thread.
JS Time spent in Javascript events. This includes event listeners, setTimeout callbacks and resolve callbacks for Promises.
RAF Time spent in requestAnimationFrame callbacks.
Swap Time spent swapping frames. This usually waits for vsync.