What is shared state?

[hyunbinseo]

• What is shared state in the following context?
• How is shared state mutated on the server?

It is recommended that you not store pre-request state in global variables, but instead use them only for cross-cutting concerns such as caching and holding database connections.

Mutating any shared state on the server will affect all clients, not just the current one.

Source: Loading, SvelteKit Documentation

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This discussion will answer #2213 (comment).

[benmccann]

state: the particular condition something is in at a specific time
shared: possessed in common with another or others

"shared state" in this context essentially means a variable shared by two different requests. Using svelte/store wouldn't be an example of shared state if you created a new instance of a store for each request, but often people will create a store as a global variable which causes it to be shared across requests

[hyunbinseo]

I have been importing store from .ts files as mentioned in #4339 (comment) and #4339 (reply in thread).

1. Would this impact static sites generated with @sveltejs/adapter-static?
2. Would this impact serverless deployments, such as Netlify or Cloudflare Workers?

I hope this use-case is implicitly mentioned in the documentation as mentioned in #4339 (reply in thread).

If your store lives in a global variable, it's a global variable and therefore is subject to the same semantics. Maybe we should also explicitly mention that this also applies to store just to make this clear.

[benmccann]

There is no code that runs on the server for a static site, so it would not apply there. Serverless sites work the same as traditional servers, so it would apply to serverless

[dominikg]

See also #4339

[hyunbinseo]

See also: What is Singleton? by Tan Li Hau