There's nothing quite so crushing as building a beautifully performant website only to have it infested with a plague of third-party scripts that add to the weight of each page and reduce the responsiveness, making a mockery of your well-considered performance budget.
Trent has been writing about this:
My latest realization is that delivering a performant, accessible, responsive, scalable website isn’t enough: I also need to consider the impact of third-party scripts.
He's started the process by itemising third-party scripts. Frustratingly though, there's rarely one single culprit that you can point to—it's the cumulative effect of "just one more beacon" and "just one more analytics script" and "just one more A/B testing tool" that adds up to a crappy experience that warms your user's hands by ensuring your site is constantly draining their battery.
Actually, having just said that there's rarely one single culprit, Adobe Tag Manager is often at the root of third-party problems. That and adverts. It's like opening the door of your beautifully curated dream home, and inviting a pack of diarrhetic elephants in: "Please, crap wherever you like."
But even the more well-behaved third-party scripts can get out of hand. Google Analytics is so ubiquitous that it's hardly even considered in the list of potentially harmful third-party scripts. On the whole, it's a fairly well-behaved citizen of your site's population of third-party scripts (y'know, leaving aside the whole surveillance capitalism business model that allows you to use such a useful tool for free in exchange for Google tracking your site's visitors across the web and selling the insights from that data to advertisers).
The initial analytics script that you—asynchronously—load into your page isn't very big. But depending on how you've configured your Google Analytics account, that might just be the start of a longer chain of downloads and event handlers.
Ed recently gave a lunchtime presentation at Clearleft on using Google Analytics—he professes modesty but he really knows his stuff. He was making sure that everyone knew how to set up goals'n'stuff.
As I understand it, there are two main categories of goals: events and destinations (there are also durations and pages, but they feel similar to destinations). You use events to answer questions like "Did the user click on this button?" or "Did the user click on that search field?". You use destinations to answer questions like "Did the user arrive at this page?" or "Did the user come from that page?"
You can add as many goals to your site's analytics as you want. That's an intoxicating offer. The problem is that there is potentially a cost for each goal you create. It's an invisible cost. It's paid by the user in the currency of JavaScript sent down the wire (I wish that the Google Analytics admin interface were more like the old interface for Google Fonts, where each extra file you added literally pushed a needle higher on a dial).
It strikes me that the event-based goals would necessarily require more JavaScript in order to listen out for those clicks and fire off that information. The destination-based goals should be able to get all the information needed from regular page navigations.
So I have a hypothesis. I think that destination-based goals are less harmful to performance than event-based goals. I might well be wrong about that, and if I am, please let me know.
With that hypothesis in mind, and until I learn otherwise, I've got two rules of thumb to offer when it comes to using Google Analytics:
- Try to keep the number of goals to a minimum.
- If you must create a goal, favour destinations over events.
This was originally posted on my own site.
There are two follow-up posts:
- Heisenberg, and
- Needs must.