How to use `some` to partially check items in object using TypeScript

Question

I have an object:

interface MYInterface {
  aaa: number;
  bbb: number;
  ccc?: number | undefined;
}

const myObject: MYInterface = {
  aaa: 0,
  bbb: 0,
  ccc: 132,
};

I want to check if some keys in this object, satisfy a condition! I'm using Array.some(...) like below:

const res = ['aaa', 'bbb'].some((key) => myObject[key] > 0)

but for myObject[key] I'm getting a TypeScript error about:

Element implicitly has an 'any' type because expression of type 'string' can't be used to index type 'INxStateCounts'.
  No index signature with a parameter of type 'string' was found on type 'INxStateCounts'.

I know that what am I trying to do is checking array of strings (keys) with objects but my array contains those keys in string.

I have tried to cast key as keyof MYInterface but no luck! I was getting so many other errors. How can I fix this?

Also my object is very big, here I use 3 properties to demonstrate the issue.

Just in case if you want to test.

Does this answer your question? Typescript get object property type from name — Peter B
– Peter B, Commented Feb 8, 2023 at 11:18
how can i use it with some(...)? That is where i stuck tbh — amdev
– amdev, Commented Feb 8, 2023 at 11:19

Anton Marinenko · Accepted Answer · 2023-02-08 11:23:31Z

3

Just make more concrete typing in your code, like this:

function someOf<T>(keys: (keyof T)[], obj: T): boolean {
  return keys.some((key) => obj[key] > 0)
}

const res = someOf(['aaa', 'bbb'], myObject);

answered Feb 8, 2023 at 11:23

Anton Marinenko

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4 Comments

amdev Over a year ago

what is the typeof T when you calling function like someOf(['aaa', 'bbb'], myObject)?

amdev Over a year ago

My understanding is MYInterface, and i should call it like someOf<MYInterface>(['aaa', 'bbb'], myObject)

amdev Over a year ago

why extracting it into function does not give you error? but having it in one line does? why i still getting error with this: (['aaa', 'bbb'] as (keyof MYInterface)[]).some(key => (myObject as MYInterface)[key] > 0)

Anton Marinenko Over a year ago

There is a simple reason for that, you have optional property ccc and it can be undefined. When it's inside the function, generic typing doesn't know about that.

Riadh Adrani · Accepted Answer · 2023-02-08 11:34:33Z

1

You can write something like this:

const keys : Array<keyof MYInterface> = ['aaa', 'bbb']

const res = keys.some((key) => (myObject[key] !== undefined && myObject[key]! > 0))

for some reason the bang ! operator is needed despite undefined checking.

answered Feb 8, 2023 at 11:34

Riadh Adrani

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2 Comments

amdev Over a year ago

actually thanks for your answer, but I don't want to use that (!), because I need to assure the correct type

Riadh Adrani Over a year ago

The ! operator assert that myObject[key] is not null/undefined.

Emilio Lucas Ceroleni · Accepted Answer · 2023-02-08 11:38:28Z

0

If you use object index signature you might get what you are looking for. Try:

interface MYInterface {
  [key:string]: number;
}
...

Other ways to approach this: How to dynamically assign properties to an object in TypeScript

answered Feb 8, 2023 at 11:38

Emilio Lucas Ceroleni

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Comments

samchan0221 · Accepted Answer · 2023-02-08 12:43:21Z

0

You can add as const to make it a tuple type. Then, the type of key argument will become 'aaa'|'bbb' instaed of string/any.

const res = (['aaa', 'bbb'] as const).some((key) => myObject[key] > 0)

answered Feb 8, 2023 at 12:43

samchan0221

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