useAtom(undefined) throws Invalid value used as weak map key

[kevinschaich]

This should be checked for or caught and re-thrown as a more helpful error message.

To Repro:

const value = useAtom(undefined)

    -> TypeError: Invalid value used as weak map key

I hit this today and if it weren't for this comment I would have been very struggling for a few hours:
#1816 (reply in thread)

One potentially common way people might hit this is if they use nested/split atoms and try to reference a key that doesn't exist.

e.g. objects:

const objectAtom = atom({
    a: atom(...)
    b: atom(...)
)

...

const bValue = useAtomValue(useAtomValue(objectAtom)[c])

e.g. lists:

const listAtom = atom([atom(...), atom(...)]

...

const thirdValue = useAtomValue(useAtomValue(listAtom)[2])

Related: #2272, #1817, #1177, #1816, #2239, #2273

[kevinschaich]

cc: @dai-shi I believe you replied to a few of the issues/discussions above.

[dai-shi]

Sure. Would you like to open a PR? Or just suggesting an improved error message may help.

I also have a question for you. Are you not using TS in this case? Because TS can warn you, we haven't prioritize this behavior much.

[kevinschaich]

I am using TypeScript but it is not bulletproof. If your signature for a dynamic object is

{ [key: string]: Atom<...> }

you could pass in any string key and Typescript will not complain until it fails at useAtom.

[dai-shi]

yeah, unless you enable noUncheckedIndexedAccess.

[kevinschaich]

This is disabled as the default and marked as not planned (microsoft/TypeScript#49169).

[kevinschaich]

Fixed in #2778