From the Microsoft post:
Timers: death by a thousand cuts
Even on a page that looks relatively quiet, below the surface there may be quite a lot of work going on. News and content sites that rely on advertisements, analytics trackers, and scroll listeners are often a good example of this. For instance, here’s a sample site illustrating some problems we often see on poorly optimized sites in the wild:
While this page is loading, and even well after it’s “settled,” there is still an enormous amount of work going on under the hood. A web page such as this one may make network requests for additional resources, or it may call
setTimeoutto queue a task for the next “tick” of the event loop. Each of these callbacks can then schedule other timeouts and network requests, starting the process anew. It’s the browser’s job to coordinate these tasks, and to ensure that they’re processed correctly along with event listeners, Promises, and any other work in accordance with the HTML5 event loop spec.
Anyway, if you were looking for one more reason to upgrade your phone (if possible) to the Creators Update then this is perhaps the nudge you needed.