multiGet return type incorrect?

[mtt87]

What happened?

👋 while using the library I noticed that multiGet has this signature:

multiGet: (keys: string[], callback?: MultiGetCallback) => Promise<readonly KeyValuePair[] | void>;

I'm not sure the return type is correct

Promise<readonly KeyValuePair[] | void>

It seems like void doesn't make sense, if I understood correctly how it works when a value doesn't exist it will return [string null] so the KeyValuePair[] is always the return type, not sure in which scenario it would return void.

I noticed it because Typescript is not happy when doing this

const values = await AsyncStorage.multiGet([ KEY1, KEY2, KEY3 ]);
setSomething(values[0][1]);

Showing this type error

Element implicitly has an 'any' type because expression of type '0' can't be used to index type 'void | readonly KeyValuePair[]'.
  Property '0' does not exist on type 'void | readonly KeyValuePair[]'.

Version

1.16.1

What platforms are you seeing this issue on?

• Android
• iOS
• macOS
• Windows
• web

System Information

n/a

Steps to Reproduce

n/a

[tido64]

I agree it's a bit weird. void doesn't really exist in JS as it would simply return undefined, or null in this case. In TypeScript, it's fine to use void for a function that may not return anything. The fix to your example is to add a check:

const values = await AsyncStorage.multiGet([ KEY1, KEY2, KEY3 ]);
if (values) {
  setSomething(values[0][1]);
}

This will allow TypeScript to narrow the type to KeyValuePair[] (since values cannot be void inside the if-statement), and you'll be able to index is as normal.

[mtt87]

@tido64 thanks for your reply

In TypeScript, it's fine to use void for a function that may not return anything.

Sure but is this really the case? Can this function not return anything?
It's 2 different things to not return anything (void or undefined or null) or return an array of KeyValuePair that has [string, null] when the key is not in the storage or [string, string] when the storage has the key.

What I'm saying here is that the library should probably change

Promise<readonly KeyValuePair[] | void>

to

Promise<readonly KeyValuePair[]>

[tido64]

Ah… Yeah, I think you're right. I was thinking of the callback, which may return null if there's an error. But for the async API, we should get a rejection, which would throw an exception. Would you mind submitting a PR with the fix? Otherwise, I can try fixing it over the weekend.

[mtt87]

I created this #767
I did it with the GitHub web UI for a quick change, let's see if all tests pass from CI 😄 otherwise I'll wait for you to do it in the weekend, you are probably more familiar with the codebase 😄

[krizzu]

🎉 This issue has been resolved in version 1.16.3 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀