Alternatively, you can install JS Paint as a PWA (Progressive Web App),
but this does not yet support offline use
(as it doesn't include a Service Worker).
It's more like a bookmark (for now), except it runs in a special window.
The user interface for installing PWAs differs by browser and operating system.
On most desktop browsers, the install prompt is in the URL bar.
On mobile, the install prompt is generally found in the menu of browser options.
See
Installing PWAs for visual guidance.