SIGX700 · Revalidation trigger threw while subscribing#

Dev message

[sigx-cache] revalidateTrigger threw while subscribing:

The thrown error is logged as a second argument, so the original stack is in the console next to the code.

What happened#

@sigx/cache tried to install its attention-revalidation trigger and the trigger function threw.

The store subscribes one "revalidate now" callback per app, lazily — on the first read that opts in with revalidateOnFocus. The trigger is the platform's: DOM focus + visibilitychange by default, or whatever cachePlugin({ revalidateTrigger }) supplied for a non-DOM runtime.

This is logged, not thrown. A cache that cannot hear about window focus is degraded, not broken — so the store marks the trigger uninstalled, logs, and carries on. Everything else keeps working: reads still fetch, staleTime still applies, invalidate() still works. What you lose is revalidation on focus; revalidateOnInterval and manual invalidation are unaffected.

Because it never throws, this one shows up in logs rather than in a stack trace, and it is easy to miss.

Fix it#

Almost always the trigger touched a global its runtime doesn't have. The default trigger installs only when a DOM is present, so this normally means a custom trigger reaching for one:

TypeScript 
// ✗ throws under lynx, terminal, or a Node/edge SSR pass
cachePlugin({
    revalidateTrigger: (revalidate) => {
        window.addEventListener('focus', revalidate);
        return () => window.removeEventListener('focus', revalidate);
    },
});

Subscribe to the event source the runtime actually has, and return its unsubscribe — whatever that runtime calls it:

TypeScript 
cachePlugin({
    revalidateTrigger: (revalidate) => {
        const subscription = appState.on('resume', revalidate);
        return () => subscription.remove();
    },
});

If the trigger has to run on more than one target, guard the capability rather than the platform name, and return nothing when there is no source to subscribe to — returning undefined is valid and simply means "nothing to unsubscribe":

TypeScript 
cachePlugin({
    revalidateTrigger: (revalidate) => {
        if (typeof document === 'undefined') return;
        document.addEventListener('visibilitychange', revalidate);
        return () => document.removeEventListener('visibilitychange', revalidate);
    },
});