ts-async-results

An Async implementation of the awesome ts-results.

For an intro into the Result's API check out the above link or Rust's own Result API.

This library only addresses the Async component of the Result.

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ts-async-results

Installation

$ npm install ts-async-results

$ yarn add ts-async-results

Usage

import { AsyncResultWrapper, AsyncErr, AsyncOk } from 'ts-async-results';

Creation

let okAsyncResult: AsyncResult<number, Error> = new AsyncOk(10);
let okResult2 = AsyncOk<number, Error>(10); // Exact same as above

let errorResult: AsyncResult<number, Error> = new AsyncOk(new Error('bad number!'));
let errorResult2 = new AsyncOk<number, Error>(new Error('bad number!')); // Exact same as above

Wrap other Result or Async Result

// From Result
new AsyncResultWrapper(new Ok(10));

// From Result Function
new AsyncResultWrapper(() => new Ok(10));

// From Result Async Function
let okFromResultAsyncFn = new AsyncResultWrapper(async () => {
    await delay(1);

    return new Ok(10)
});

// From Async
new AsyncResultWrapper(new AsyncOk(10));

// From Async Result Function
new AsyncResultWrapper(() => new AsyncOk(10));

// From Async Result Async Function :)
new AsyncResultWrapper(async () => {
    await delay(1);

    return new AsyncOk(10)
});

// Works in the same way with AsyncErr or the alias AsyncReult.toAsyncResult()

Map and MapErr

const httpAsyncResult = new AsyncResultWrapper(async () => {
    try {
      const { data } = await http.get('/api');

      return new Ok(data)
    } catch (e) {
      return new Err('BadRequest');
    }
  });

httpAsyncResult
    .map((myData) => {
        // do stuff with the data
    })
    .mapErr((err) => {
        console.error(err);
    });

Flatmap

const getResourceAsyncResult = () => new AsyncResultWrapper(async () => {
    try {
      const { data } = await http.get('/api');

      return new Ok(data)
    } catch (e) {
      return new Err('BadRequest');
    }
  });

const postResourceAndAnotherAsyncResult = (id: string) => new AsyncResultWrapper(async () => {
    try {
      const { data } = await http.post('/api', { id });

      return new Ok(data)
    } catch (e) {
      return new Err('BadRequest');
    }
  });


getResourceAsyncResult()
    .flatMap((myData) => {
        // do some more async stuff with the data and return another AsyncResult
        return postResourceAndAnotherAsyncResult(myData.id);
    })
    .map((myData) => {
        // do stuff with the data
    })
    .mapErr((err) => {
        console.error(err);
    });

FlatMapErr

const getResourceAsyncResultWithRetry = () => new AsyncResultWrapper(async () => {
    try {
        const { data } = await http.get('/api');

        return new Ok(data)
    } catch (e) {
        return new Err('BadRequest');
    }
  })
  .flatMapErr((err) => {
        // you can intercept an Err path and transform it into a (potential) Ok path

        if (err === 'CONNECTION_FAILED') {
            const retryAttemptAsyncResult = getResourceAsyncResult();


            // If the attempt failed due to a network error automatically retry
            // NOTE: Don't use this code in production as it's veeeery inefficient!
            //       It's only meant for demonstration purposes.
            return retryAttemptAsyncResult;
        }
        else {
            // We always return back an AsyncResult
            return new AsyncErr(err);
        }
    });

getResourceAsyncResultWithRetry()
    .map((myData) => {
        // do stuff with the data
    })
    .mapErr((err) => {
        console.error(err);
    });

Expect

To use Expect we make use of the fact that an AsyncResult resolves to a simple Result.

let goodAsyncResult = new AsyncOk(1);
let badAsyncResult = new AsyncErr("something went wrong");

let goodResult = (await goodAsyncResult.resolve());
let badResult = (await goodAsyncResult.resolve());

goodResult.expect('goodResult should be a number'); // 1
badResult.expect('badResult should be a number'); // throws Error("badResult should be a number - Error: something went wrong")

Empty

function checkIsValid(isValid: boolean): AsyncResult<void, Error> {
    if (isValid) {
        return AsyncOk.EMPTY;
    } else {
        return new AsyncErr("Not valid");
    }
}

Resolve

Calling myAsyncResult.resolve() transforms it into a Promise<Result<T, E>>

Ok Path

let asyncResult = new AsyncOk(1);

let result = (await goodAsyncResult.resolve());

console.log(result.val); // 1

Error Path

Note: Calling resolve() does NOT throw when the value is an Error. See ResolveUnwrap if you need that behavior

let asyncResult = new AsyncErr('SimpleErr');

let result = (await goodAsyncResult.resolve());

console.log(result.val); // SimpleErr

Unwrap

To use Unwrap we make use of the fact that an AsyncResult resolves to a simple Result.

let goodAsyncResult = new AsyncOk(1);
let badAsyncResult = new AsyncErr("something went wrong");

let goodResult = (await goodAsyncResult.resolve());
let badResult = (await goodAsyncResult.resolve());

goodResult.unwrap(); // 1
badResult.unwrap(); // throws Error("something went wrong")

UnwrapOr

To use UnwrapOr we make use of the fact that an AsyncResult resolves to a simple Result.

let goodAsyncResult = new AsyncOk(1);
let badAsyncResult = new AsyncErr("something went wrong");

let goodResult = (await goodAsyncResult.resolve());
let badResult = (await goodAsyncResult.resolve());

let goodResult = Ok(1);
let badResult = Err(new Error("something went wrong"));

goodResult.unwrapOr(5); // 1
badResult.unwrapOr(5); // 5

ResolveUnwrap

Combines Resolve and Unwrap functionalities.

let goodAsyncResult = new AsyncOk(1);
console.log(await goodAsyncResult.resolveUnwrap()); // 1

let badAsyncResult = new AsyncErr("something went wrong");
console.log(await badAsyncResult.resolveUnwrap()); // throws Error("something went wrong")

ResolveUnwrapOr

Similar to "ResolveUnwrap" but provides a fallback for the Error path. The Ok path remains unaffected!

let goodAsyncResult = new AsyncOk(1);
console.log(await goodAsyncResult.resolveUnwrapor(5)); // 1

let badAsyncResult = new AsyncErr("something went wrong");
console.log(await badAsyncResult.resolveUnwrapOr(5)); // 5

Combining Results

ts-async-results has one helper function for operating over n Result objects.

AsyncResult.all

Either returns all of the Ok values, or the first Err value