I am creating a WebExtension for browsers. So I found out about the browser.alarms API. It basically allows you to set a (reoccurring or one-time) alarm and a callback will be fired.
Now, we've had such a feature this for a long time in JavaScript as in setTimeout and setInterval. So what is the difference to these ones? Why or in what cases may I prefer the one over the other?
I mean the main difference is obvious: You can only refire it e.g. in minutes, not seconds. Although, I think with when you can also unregister and re-register it in millisecond precision, but I think the API may be intended for longer periods, i.e. minutes. (I am just guessing here.)
So why should I use it instead of a simple setInterval/setTimeout callback?
setTimeout/setInterval time span is limited by 2^31-1 = 2147483647 i.e. ~24 days. Values less than 0 or bigger than that are cast into int32 range, which can produce unexpected results.
setTimeout/setInterval is part of standard DOM, not the isolated world, so when you use it inside a content script, the web page script can clear them accidentally via clearTimeout/clearInterval.
Workaround: post a message to the background script so it sets the timer and sends a response upon finishing.
Event pages (those that have "persistent": false in manifest.json) won't wait for setTimeout / setInterval before unloading due to inactivity and won't wake up for such a timer so you can only use them for a very short time (currently the event pages are guaranteed to live for 5 seconds).
Within these designated limits you can safely use setTimeout/setInterval.