Is there a syntax available for type annotation of arrays created from pre-declared variables?

Question

Is there a syntax available for type annotation of arrays created from pre-declared variables?

According to my standards, all possible annotations are required in TypeScript. Therefore, TypeScript-ESLint is prompting me to annotate the `[ responseData, cognitoUser ]`. However, when I try to use the syntax `[ responseData1: ResponseData1, responseData2: ResponseData2]`, I receive an error message (`TS1005: ';' expected`). If this syntax doesn't work, it might be an issue with the TypeScript/ESLint repository.

let responseData1: ResponseData1;
let responseData2: ResponseData2;

try {
  [ responseData1, responseData2] = await Promise.all([ /* ... */ ])
} catch {
 // ...
}

typescript typescript-eslint

Answer 1

Answer №1

In TypeScript 4, it's now possible to include labels for array types.

type DataResponse = [data1: DataResponse1, data2: DataResponse2];

This feature can be utilized when using Promise.all:

try {
  const [data1, data2]: DataResponse = await Promise.all([ /* ... */ ]);
} catch {
 // Handle error
}

Answer 2

In TypeScript 4, it's now possible to include labels for array types.

type DataResponse = [data1: DataResponse1, data2: DataResponse2];

This feature can be utilized when using Promise.all:

try {
  const [data1, data2]: DataResponse = await Promise.all([ /* ... */ ]);
} catch {
 // Handle error
}

Answer 3

Answer №2

When using destructuring with Promise.all, it is important to follow this overall pattern and handle errors:

function fetchNumber(): Promise<number> {
  return Promise.resolve(2);
}

function retrieveNumber(): Promise<number> {
  return Promise.resolve(3);
}

async function combineResults(): Promise<{ fetched: number; retrieved: number }> {
  try {
    const [fetched, retrieved] = await Promise.all([fetchNumber(), retrieveNumber()]);
    return { fetched, retrieved };
  } catch (error) {
    throw new Error("An error occurred while combining results.");
  }
}

Answer 4

When using destructuring with Promise.all, it is important to follow this overall pattern and handle errors:

function fetchNumber(): Promise<number> {
  return Promise.resolve(2);
}

function retrieveNumber(): Promise<number> {
  return Promise.resolve(3);
}

async function combineResults(): Promise<{ fetched: number; retrieved: number }> {
  try {
    const [fetched, retrieved] = await Promise.all([fetchNumber(), retrieveNumber()]);
    return { fetched, retrieved };
  } catch (error) {
    throw new Error("An error occurred while combining results.");
  }
}

Is there a syntax available for type annotation of arrays created from pre-declared variables?

Answer №1

Answer №2

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