Schizophrenia from the business side who want metrics on TTFB and TTI but also want to have a firehose of information about users and don't connect that there are real performance costs to gathering this information.
Giant dependencies and time to interactive have been battling each other for decades. It's not just how much code you run on first paint, that's a discipline in its own right. But until the javascript and CSS load you don't really control much of anything in the browser lifecycle.
So you work and work on those, and you've gotten through a bunch of performance-as-feature gates, but then someone throws three analytics packages on that together are proportional to the code you sweated to carve out of the initial payloads. You can usually defer those, but how easy that was depends on which generation of web browser you're talking about.
What you can't control is how much work those libraries due on the page while they bootstrap. As recently as the last project I worked on in my current job, I discovered that something like 60% of the event loop blocking was coming from some analytics library that was stuck in a reflow loop that was taking longer than we had saved on code that a couple of my poor coworkers had been working on for ages, to the point you could hear the exhaustion in their voices in standup.
That one was mostly tripping up due to a performance bug in an old version of jquery (mutation on read), but other examples in this problem domain are often not so simple to fix.
Ultimately this is a social problem, but I've seen it way too many times.Someone high in the org chart didn't insist that we run the application exactly as it would run in production. In a Saas situation a customer may say "I want to be able to add stuff to my pages, can you do that?" and nobody catches on that they want to run analytics, and not just for one dashboard, but for the old one they can't let go of and the new one that is cooler but only answers 80% of their questions. And then they want a third party live chat which is somehow as slow as the two analytics libraries combined.
I have ran into similar experiences at a prior job. It was wonderful when I finally convinced our C-level that we should rip out all 3rd party tracking and it materialized in a 1-2 second Time to Interactive boost. It really does make a huge difference in user experience when you are able to prevent this stuff from bloating your websites.
Giant dependencies and time to interactive have been battling each other for decades. It's not just how much code you run on first paint, that's a discipline in its own right. But until the javascript and CSS load you don't really control much of anything in the browser lifecycle.
So you work and work on those, and you've gotten through a bunch of performance-as-feature gates, but then someone throws three analytics packages on that together are proportional to the code you sweated to carve out of the initial payloads. You can usually defer those, but how easy that was depends on which generation of web browser you're talking about.
What you can't control is how much work those libraries due on the page while they bootstrap. As recently as the last project I worked on in my current job, I discovered that something like 60% of the event loop blocking was coming from some analytics library that was stuck in a reflow loop that was taking longer than we had saved on code that a couple of my poor coworkers had been working on for ages, to the point you could hear the exhaustion in their voices in standup.
That one was mostly tripping up due to a performance bug in an old version of jquery (mutation on read), but other examples in this problem domain are often not so simple to fix.
Ultimately this is a social problem, but I've seen it way too many times.Someone high in the org chart didn't insist that we run the application exactly as it would run in production. In a Saas situation a customer may say "I want to be able to add stuff to my pages, can you do that?" and nobody catches on that they want to run analytics, and not just for one dashboard, but for the old one they can't let go of and the new one that is cooler but only answers 80% of their questions. And then they want a third party live chat which is somehow as slow as the two analytics libraries combined.