TypeError when updating $session in component constructor

[sfriedel]

Describe the bug
If the $session store gets written to in the component constructor of a route, sveltekit throws a TypeError at https://github.com/sveltejs/kit/blob/master/packages/kit/src/runtime/client/renderer.js#L115

Logs

start.js:448 Uncaught (in promise) TypeError: Cannot read property 'parse' of null

To Reproduce

• git clone -b typeerror-during-session-hydration git@github.com:sfriedel/sveltekit-bugreport.git
• pnpm install
• pnpm dev
• open http://localhost:3000/ in the browser
• you should see the exception from above in the JS error logs
• check src/routes/index.svelte for the code that triggers the error

Expected behavior
No exception should be thrown

Stacktraces

Stack trace

start.js:448 Uncaught (in promise) TypeError: Cannot read property 'parse' of null
at Array. (start.js:448)
at Object.set (index.mjs?v=93707a36:35)
at set_store_value (index.mjs?v=93707a36:136)
at instance (index.svelte? [sm]:9)
at init (index.mjs?v=93707a36:1485)
at new Routes (index.svelte? [sm]:10)
at createProxiedComponent (svelte-hooks.js:245)
at new ProxyComponent (proxy.js:241)
at new Proxy (proxy.js:341)
at create_if_block_2 (root.svelte? [sm]:38)

Information about your SvelteKit Installation:

Diagnostics

System: OS: Linux 5.8 Ubuntu 20.10 (Groovy Gorilla) CPU: (8) x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz Memory: 1.31 GB / 15.34 GB Container: Yes Shell: 5.8 - /bin/zsh Binaries: Node: 14.17.0 - /usr/bin/node Yarn: 1.22.5 - /usr/bin/yarn npm: 6.14.13 - /usr/bin/npm Watchman: 4.9.0 - /home/sef/.local/opt/watchman/bin/watchman Browsers: Chrome: 90.0.4430.212 Firefox: 89.0 npmPackages: @sveltejs/kit: next => 1.0.0-next.115 svelte: ^3.34.0 => 3.38.2

Severity
Low. I have a workaround in place: deferring the store updates with a simple setTimeout(..., 0) seems to avoid the issue.

[gxcodes]

Was about to write an issue but saw this. It happened on fresh init npm init svelte@next and choose skeleton. Import {session} and {browser} then set value to $session trigger the TypeError loking for url route.

Low. I have a workaround in place: deferring the store updates with a simple setTimeout(..., 0) seems to avoid the issue.

Thanks @sfriedel, confirmed also this workaround somehow worked: setTimeout(() => $session = ... )

[ajwinkworth]

I also have an issue with the same code but I am calling session.set() in a async click event handler after doing a fetch to an endpoint.

The setTimeout() workaround did not work for me. App still seems to function fine.

[benmccann]

Posting a link to the reproduction repo here for ease of access: https://github.com/sfriedel/sveltekit-bugreport/tree/typeerror-during-session-hydration