ts-results

A typescript implementation of Rust's Result object. Brings compile-time error checking to typescript.

Note: This is the documentation for the newly released [email protected] with breaking changes. To see breaking changes, go to CHANGELOG.md

Installation
Example
Usage
- Creation
- Type Safety
- Unwrap
- Expect
- Map, MapErr
- Else
- UnwrapOr
- Empty
- Combining Results
  - Result.all
  - Result.any
Usage with rxjs

Installation

$ npm install ts-results

$ yarn add ts-results

Example

Convert this:

import {existsSync, readFileSync} from 'fs';

function readFile(path: string): string {
    if (existsSync(path)) {
        return readFileSync(path);
    } else {
        // Callers of readFile have no way of knowing the function can fail
        throw new Error('invalid path');
    }
}
// This line may fail unexpectedly without warnings from typescript
const text = readFile('test.txt');

To this:

import {existsSync, readFileSync} from 'fs';
import {Ok, Err, Result} from 'ts-results';

function readFile(path: string): Result<string, 'invalid path'> {
    if (existsSync(path)) {
        return new Ok(readFileSync(path)); // new is optional here
    } else {
        return new Err("invalid path"); // new is optional here
    }
}

// Typescript now forces you to check whether you have a valid result at compile time.
const result = readFile('test.txt');
if (result.ok) {
    // text contains the file's content
    const text = result.val;
} else {
    // err equals 'invalid path'
    const err = result.val;
}

Usage

import { Result, Err, Ok } from 'ts-results';

Creation

let okResult: Result<number, Error> = Ok(10);
let okResult2 = Ok<number, Error>(10); // Exact same as above

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

Type Safety

let result = Ok<number, Error>(1);
if (result.ok) {
    // Typescript knows that result.val is a number because result.ok was true
    let number = result.val + 1;
} else {
    // Typescript knows that result.val is an Error because result.ok was false
    console.error(result.val.message);
}

if (result.err) {
    // Typescript knows that result.val is an Error because result.err was true
    console.error(result.val.message);
} else {
    // Typescript knows that result.val is a number because result.err was false
    let number = result.val + 1;
}

Unwrap

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

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

Expect

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

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")

Map and MapErr

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

goodResult.map(num => num + 1).unwrap(); // 2
badResult.map(num => num + 1).unwrap(); // throws Error("something went wrong")

goodResult.map(num => num + 1).mapErr(err => new Error('mapped')).unwrap(); // 2
badResult.map(num => num + 1).mapErr(err => new Error('mapped')).unwrap(); // throws Error("mapped")

Else

Deprecated in favor of unwrapOr

UnwrapOr

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

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

Empty

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

Combining Results

ts-results has two helper functions for operating over n Result objects.

Result.all

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

let pizzaResult: Result<Pizza, GetPizzaError> = getPizzaSomehow();
let toppingsResult: Result<Toppings, GetToppingsError> = getToppingsSomehow();

let result = Result.all(pizzaResult, toppingsResult); // Result<[Pizza, Toppings], GetPizzaError | GetToppingsError>

let [pizza, toppings] = result.unwrap(); // pizza is a Pizza, toppings is a Toppings.  Could throw GetPizzaError or GetToppingsError.

Result.any

Either returns the first Ok value, or all Err values

let url1: Result<string, Error1> = attempt1();
let url2: Result<string, Error2> = attempt2();
let url3: Result<string, Error3> = attempt3();

let result = Result.any(url1, url2, url3); // Result<string, Error1 | Error2 | Error3>

let url = result.unwrap(); // At least one attempt gave us a successful url

Usage with rxjs

resultMap

Allows you to do the same actions as the normal rxjs map operator on a stream of Result objects.

import {of, Observable} from 'rxjs';
import {Ok, Err, Result} from 'ts-results';
import {resultMap} from 'ts-results/rxjs-operators';

const obs$: Observable<Result<number, Error>> = of(Ok(5), Err('uh oh'));

const greaterThanZero = obs$.pipe(
  resultMap(number => number > 0), // Doubles the value
); // Has type Observable<Result<boolean, 'uh oh'>>

greaterThanZero.subscribe(result => {
  if (result.ok) {
    console.log('Was greater than zero: ' + result.val);
  } else {
    console.log('Got Error Message: ' + result.val);
  }
});

// Logs the following: 
// Got number: 10
// Got Error Message: uh oh

resultMapErr

import {resultMapErr} from 'ts-results/rxjs-operators';

Behaves exactly the same as resultMap, but maps the error value.

resultMapTo

import {resultMapTo} from 'ts-results/rxjs-operators';

Behaves the same as resultMap, but takes a value instead of a function.

resultMapErrTo

import {resultMapErrTo} from 'ts-results/rxjs-operators';

Behaves the same as resultMapErr, but takes a value instead of a function.

elseMap

Allows you to turn a stream of Result objects into a stream of values, transforming any errors into a value.

Similar to calling the else function, but works on a stream of Result objects.

import {of, Observable} from 'rxjs';
import {Ok, Err, Result} from 'ts-results';
import {elseMap} from 'ts-results/rxjs-operators';

const obs$: Observable<Result<number, Error>> = of(Ok(5), Err(new Error('uh oh')));

const doubled = obs$.pipe(
  elseMap(err => {
    console.log('Got error: ' + err.message);
    
    return -1;
  })
); // Has type Observable<number>

doubled.subscribe(number => {
  console.log('Got number: ' + number);
});

// Logs the following:
// Got number: 5
// Got error: uh oh
// Got number: -1

elseMapTo

import {elseMapTo} from 'ts-results/rxjs-operators';

Behaves the same as elseMap, but takes a value instead of a function.

resultSwitchMap and resultMergeMap

Allows you to do the same actions as the normal rxjs switchMap and rxjs switchMap operator on a stream of Result objects.

Merging or switching from a stream of Result<T, E> objects onto a stream of <T2> objects turns the stream into a stream of Result<T2, E> objects.

Merging or switching from a stream of Result<T, E> objects onto a stream of Result<T2, E2> objects turn the stream into a stream of Result<T2, E | T2> objects.

import {of, Observable} from 'rxjs';
import {Ok, Err, Result} from 'ts-results';
import {resultMergeMap} from 'ts-results/rxjs-operators';

const obs$: Observable<Result<number, Error>> = of(new Ok(5), new Err(new Error('uh oh')));

const obs2$: Observable<Result<string, CustomError>> = of(new Ok('hi'), new Err(new CustomError('custom error')));

const test$ = obs$.pipe(
  resultMergeMap(number => {
    console.log('Got number: ' + number);

    return obs2$;
  })
); // Has type Observable<Result<string, CustomError | Error>>

test$.subscribe(result => {
  if (result.ok) {
    console.log('Got string: ' + result.val);
  } else {
    console.log('Got error: ' + result.val.message);
  }
});

// Logs the following:
// Got number: 5
// Got string: hi
// Got error: custom error
// Got error: uh oh

filterResultOk

Converts an Observable<Result<T, E>> to an Observble<T> by filtering out the Errs and mapping to the Ok values.

import {of, Observable} from 'rxjs';
import {Ok, Err, Result} from 'ts-results';
import {filterResultOk} from 'ts-results/rxjs-operators';

const obs$: Observable<Result<number, Error>> = of(new Ok(5), new Err(new Error('uh oh')));

const test$ = obs$.pipe(
  filterResultOk()
); // Has type Observable<number>

test$.subscribe(result => {
  console.log('Got number: ' + result);
});

// Logs the following:
// Got number: 5

filterResultErr

Converts an Observable<Result<T, E>> to an Observble<T> by filtering out the Oks and mapping to the error values.

import {of, Observable} from 'rxjs';
import {Ok, Err, Result} from 'ts-results';
import {filterResultOk} from 'ts-results/rxjs-operators';

const obs$: Observable<Result<number, Error>> = of(new Ok(5), new Err(new Error('uh oh')));

const test$ = obs$.pipe(
  filterResultOk()
); // Has type Observable<number>

test$.subscribe(result => {
  console.log('Got number: ' + result);
});

// Logs the following:
// Got number: 5

petehunt / ts-results Goto Github PK

ts-results's Introduction