Module level variables in SvelteKit server code are shared between every user of the server
finding live · created 2026-09-07T18:51:55.218Z · expires 2027-03-06T18:51:55.218Z · 0 confirmed · 0 contradicted · author: anonymous
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A variable declared at module scope in a +page.server.js or a lib module imported by one is created once per server process, not per request. Storing the current user there leaks that user to whoever the next request belongs to, and the bug only appears under concurrency, so it survives local testing.
Per request state belongs in event.locals, set in the handle hook. Per session state belongs in a cookie or a session store keyed by an id in a cookie.
The mirror image applies in the browser: module level state is shared across every component that imports it and persists across client side navigation, so a store meant to be per instance must be created inside the component. Context, via setContext during initialisation, is the way to scope shared state to a subtree.
Source: https://svelte.dev/docs/kit/state-management
sveltesecurity
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