Object.values creates variables implicitly typed as any with no warning, even with noImplicitAny

[guillaumebrunerie]

Bug Report

In some cases, Object.values creates variables implicitly typed as any without any warning, even though noImplicitAny is set to true.

🔎 Search Terms

Object.values, any, noImplicitAny

🕗 Version & Regression Information

• This is the behavior in every version I tried (including 4.8.0 beta in the Playground), and I reviewed the FAQ for entries about any/unknown/Object.values

⏯ Playground Link

Playground link with relevant code

💻 Code

declare const obj : {[key: string]: string} | {[key: string]: number}

for (const v of Object.values(obj)) {
    v.a.b.c = 42; // No error or warning, v has type any
}

🙁 Actual behavior

v has type any even though I never wrote any myself and set the noImplicityAny option to true.

🙂 Expected behavior

Ideally v should have type string | number, but at the very least it should either have type unknown or trigger an "implicit any" warning.

[MartinJohns]

The signature of Object.values() returns an explicit any (intentionally), there's nothing implicit. Changing it to unknown would be a massive breaking change, which IMO would be pointless, as this method is explicitly for dealing with dynamic data. But I understand the sentiment, tho it would be a feature request instead of a bug.

[guillaumebrunerie]

Note that Object.values does not always return an explicit any. For instance if its argument is of type {[key: string]: (string | number)} (to which the type in my original example is assignable), then it does return (string | number)[] as I would expect:

declare const obj : {[key: string]: string} | {[key: string]: number}

const obj2: {[key: string]: string | number} = obj;

for (const v of Object.values(obj2)) {
    v.a.b.c = 42; // Error: Property 'a' does not exist on type 'string | number'.
}

This made it particularly surprising to me as I used Object.values several times before without having to deal with any, but suddenly I have an any appearing just because my variable happens to be of a union type.
Maybe the non-any type signature of Object.values could be refined to also deal with union types properly?

Also, I would argue that unknown is the correct type for dealing with dynamic data, but I agree that it could be a big breaking change.

[MartinJohns]

Note that Object.values does not always return an explicit any. For instance if its argument is of type {[key: string]: (string | number)} (to which the type in my original example is assignable), then it does return (string | number)[] as I would expect:

That's true, I always forget that, because it really shouldn't do that. It should always return any or unknown. See #38520.

[guillaumebrunerie]

Ah, thank you for the link, makes perfect sense now, I didn’t realize this type was actually inconsistent. I guess I'll try to avoid Object.values from now on 😄