CODEWITHSUNDEEP
genericstypescripttypestypescript2.0
rid
rid

Reputation: 63610

Generic type of object value parameter

function getValues<T, U extends { [key: string]: T }>(object: U): T[] {
    // ...
}

const test = { a: 123, b: 234 };
const values = getValues(test);

In the above code, I expect values to be of type number[], but the actual type is {}[].

What am I doing wrong?

Upvotes: 1

Views: 1287

Answers (1)

Nitzan Tomer
Nitzan Tomer

Reputation: 164457

The type for this { a: 123, b: 234 } object is:

{ a: number; b: number; }

And not

{ [key: string]: number }

You can do:

const test = { "a": 123, "b": 234 } as { [key: string]: number };

To tell the compiler that it's indeed what you want.
But even then you still won't get the type you want for values:

const values = getValues(test); // type of values {}[]

You should do:

function getValues<T>(object: { [key: string]: T }): T[] {
    return null;
}

const test = { "a": 123, "b": 234 } as { [key: string]: number };
const values = getValues(test);

(code in playground)

Upvotes: 2

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