Obtain specific data from a multi-type array that is being returned

Question

Obtain specific data from a multi-type array that is being returned

I am working with a function/hook that returns an array containing values of type boolean and MyErrorType

export declare const getErrorData: () => readonly [ boolean, MyErrorType ];

There are instances where I only need the 2nd value in the array, which is of type MyErrorType. I'm looking for a cleaner way to retrieve this specific value. Currently, the only solution I have found is accessing the 2nd element directly from the array like this:

const error = getErrorData()[1];

Is there a method to extract the array element based on the variable type? For example:

const error: MyErrorType = getErrorData();

typescript

Answer 1

Answer №1

Modifying the functionality of a program based on types is not possible with Typescript, as it eliminates types during compilation and only executes the resulting Javascript code.

An alternative approach, as mentioned by @tymzap, is to return an object instead of an array. Another technique is to employ destructuring:

const [, error] = getErrorData();

Answer 2

Modifying the functionality of a program based on types is not possible with Typescript, as it eliminates types during compilation and only executes the resulting Javascript code.

An alternative approach, as mentioned by @tymzap, is to return an object instead of an array. Another technique is to employ destructuring:

const [, error] = getErrorData();

Answer 3

Answer №2

While this may not directly address your inquiry, it presented an interesting challenge in creating a type that iterates through an array and returns the index of an expected type. Here is the purely defined type:

Link to TypeScript playground

Condensed version:

type GrabIndexOfType<
  T,
  A extends any[] | readonly any[],
  Curr extends number = A["length"],
  Idx extends number = 0,
> = Curr extends 1
  ? A[0] extends T 
    ? Idx
    : never
  : A extends [any, ... infer Rest] | readonly [any, ... infer Rest]
    ? GrabIndexOfType<T, [... Rest], SubOne<Curr>, AddOne<Idx>>
    : never
;

type Tuple<N extends number, T extends any[] = []> = T["length"] extends N
  ? T
  : Tuple<N, [... T, any]>;

type AddOne<A extends number> = Tuple<A> extends [... infer U] ? [any, ... U]["length"] : never;

type SubOne<A extends number> = Tuple<A> extends [
  ...infer U,
  any
]
  ? U["length"]
  : never;

type b = GrabIndexOfType<MyErrorType, ReturnType<typeof getErrorData>>;

Answer 4

While this may not directly address your inquiry, it presented an interesting challenge in creating a type that iterates through an array and returns the index of an expected type. Here is the purely defined type:

Link to TypeScript playground

Condensed version:

type GrabIndexOfType<
  T,
  A extends any[] | readonly any[],
  Curr extends number = A["length"],
  Idx extends number = 0,
> = Curr extends 1
  ? A[0] extends T 
    ? Idx
    : never
  : A extends [any, ... infer Rest] | readonly [any, ... infer Rest]
    ? GrabIndexOfType<T, [... Rest], SubOne<Curr>, AddOne<Idx>>
    : never
;

type Tuple<N extends number, T extends any[] = []> = T["length"] extends N
  ? T
  : Tuple<N, [... T, any]>;

type AddOne<A extends number> = Tuple<A> extends [... infer U] ? [any, ... U]["length"] : never;

type SubOne<A extends number> = Tuple<A> extends [
  ...infer U,
  any
]
  ? U["length"]
  : never;

type b = GrabIndexOfType<MyErrorType, ReturnType<typeof getErrorData>>;

Obtain specific data from a multi-type array that is being returned

Answer №1

Answer №2

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