Hacker News Reader

I wonder if this is due to how background tab javascript execution is restricted when not in focus

Same in Safari. It's pretty cool actually. In the demo, it does as you say when you switch tabs: plays a few more notes in the right channel, then holds the left in a loop of the last sample.

In a real app you'd definitely want to mute based on losing focus.

My guess is that track.processMusic(); isn't being called unless the tab is visible.