Synchronizing with Effects - discussion (2023-02-03)
The "Synchronizing with Effects" page is one of the clearest explanations of what effects are for: keeping your component in sync with something outside React. In practice, teams still use effects for everything. I'm curious what people have found works to keep effects small, testable, and observable—especially in apps that lean on explicit lanes and evidence keys.
What effect patterns do you actually keep (subscriptions, timers, DOM) and what do you push into derived state or handlers? How do you make effect cleanup behavior understandable under rapid identity changes? Do you log effect transitions as contract lines, and if so, what do you include (reason, lane, identity)?
Comments (16)
Back to latestThe best constraint for us: effects must touch something external. If it's internal, it probably shouldn't be an effect.
That rule alone removed a lot of state-sync bugs.
We treat effect lifecycle as lanes and we log transitions so cleanup isn't mysterious:
txt
[tips] effect=subscribe:socket lane=pending identity=room:general reason=mount
[tips] effect=subscribe:socket lane=ok identity=room:general reason=open
[tips] effect=subscribe:socket lane=cleanup identity=room:general reason=identityChange to=room:randomThat last line prevents the classic "why did it disconnect" mystery.
Counterpoint: effects are often used because the model isn't explicit enough.
Teams keep adding effects to patch behavior. The real fix is clarifying the contract (lane, intent, identity).
Yes. A lot of effect complexity disappears when identity boundaries are explicit.
If the state machine is clear, the effect can just execute one transition.
Cleanup under rapid changes was easier when we treated cleanup as success, not as a failure path.
If cleanup is logged as a normal lane transition, it's not scary anymore.
Long-form argument: effects become dangerous when they create implicit order dependencies (effect A must run before effect B).
If you need ordering, you need an orchestration contract (named flow) rather than two independent effects hoping the scheduler cooperates.
Timers and intervals are the biggest footgun. We only allow them behind a tick posture contract and we render it:
txt
[tips] tick=warm intervalMs=5000 reason=default
[tips] tick=hot intervalMs=1000 reason=user:activeDOM measurement effects are fine as long as you make them deterministic and bounded.
We measure on identity boundaries (content change, resize) and log the trigger reason.
Counterpoint: sometimes you do want to sync internal derived state (e.g. building a cache) and effects are convenient.
But if you do it, treat it as a derive contract and centralize it so multiple components don't compete.
The page also helps prevent "fetch in effect then setState" habits.
If your data posture is explicit and you render lanes, you can avoid a lot of timing bugs.
Docs tie-in: effects are much easier to reason about when the app has an evidence layer.
Related: Testing and Debugging and Performance and Rendering (Best Practices).
We made a guideline: effects must include an explicit identity string in their log (even if it's "global").
It prevented effects that accidentally capture stale closures without noticing.
Long-form counterpoint: lots of teams use effects because they want "after render" semantics for UI changes.
Sometimes that's real, but often it's hiding a missing intent boundary. If the intent boundary is explicit (click, blur, route change), you can do the work there.
Effect cleanup got easier when we treated cleanup as idempotent and safe to run multiple times.
If cleanup can run twice without breaking, rapid identity changes stop being scary.
We also render a compact data-last-effect and data-last-effect-reason string.
It's a small thing but it turns "why did it do that" into an answerable question.
The page is basically: use effects as bridges, not as brains.
Once you accept that, the right architecture decisions tend to follow.
If you want to keep effects small, name them like APIs and require each one to have evidence.
That rule makes it hard to write a giant effect that does five things.