Tests if setInterval is slowed down or suspended when user goes to another browser tab / window. When interval is running, every 300 ms counter in page title should increase.

To run with_worker.html you need to use a HTTP server running locally, because simply opening file (by file:// ...) will block access to the worker file. I used http-server local server running on Node.js that displays the file under http://localhost:8080/no_worker.html and http://localhost:8080/with_worker.html respectively.

The results are so far:

• Firefox 57.0, Mac Sierra - main JS slowed down, Web Worker working normally
• Chrome 63.0, Mac Sierra - main JS slowed down, Web Worker working normally
• Safari 11.0, Mac Sierra - main JS slowed down after ~2 s, Web Worker slowed down after some longer time (~20 s)