Third-party JS isn't behind sites that perform so badly they make the whole system slow down even when you're not on the page, or eat memory like it's free. Bot

Third-party JS isn't behind sites that perform so badly they make the whole system slow down even when you're not on the page, or eat memory like it's free. Both those things can happen on sites that aren't "apps" at all, or that don't need to be as huge and wasteful as they are to achieve the same levels of "app-ness" that they have (gmail is a notable offender in the latter category, but it's far from the only one). Those problems are largely due to really bad judgement, in first-party code, about where (and whether) to attach Javascript event listeners, terrible use of timers, and all manner of programmer-productivity-and-QOL enhancements that invariably (it seems) manifest as much higher end-user memory use and lots of bad (for performance) memory access patterns.