Base Ts Result

Better error handling stolen from rust. Return result values instead of throwing exceptions. Handle every error result with minimum nesting.

• Install
• Example
• Docs
  • Constructors
  • Result
  • AsyncResult
  • Helpers
• Sources

Install

npm i base-ts-result
yarn add base-ts-result
pnpm add base-ts-result

Example

import { Ok, Err, type Result } from 'base-ts-result';

const gonnaThrow = () => {
    throw new Error("you have to catch me or i'll crash the app");
};

const res = toResult(gonnaThrow);
res.isErr() // true

/**
 * @description returns random value, returns error if the value <= 0.5
 */
const getRes = (): Result<number, string> => {
    const val = Math.random();

    if (val > 0.5) {
        return Ok(val);
    }

    return Err('number is too low');
};

/**
 * @description returns random value or zero if random value <= 0.5
 */
const handleRes = () => {
    return getRes()
        .inspect(v => console.log(`Got ok value ${v}`))
        .inspectErr(e => console.error(e))
        .unwrapOr(0);
};

const val = handleRes();
console.log(val);

Docs

Constructors

Handy functions to create Result objects

import { Ok, Err } from 'base-ts-result';

// create success Result
const okRes = Ok('success');

// create error Result
const errRes = Err('failure');

Result

Interface that contains operation result and interaction methods

Result.unwrap()

Unwraps result value or throws an error if the result is Err.

import { Ok, Err } from 'base-ts-result';

let res = Ok('great success');
console.log(res.unwrap());

res = Err('fatal error');
res.unwrap(); // throws an error

Result.unwrapErr()

Unwraps result error or throws an error if the result is Ok.

import { Ok, Err } from 'base-ts-result';

let res = Ok('great success');
res.unwrapErr(); // throws an error

res = Err('fatal error');
res.unwrapErr(); // return the error

Result.unwrapOr(altValue)

Unwraps original value or replaces it with provided alternative if the result is Err.

import { Ok, Err } from 'base-ts-result';

let res = Ok('great success');
console.log(res.unwrapOr('not that great')); // prints great success

res = Err('fatal error');
console.log(res.unwrapOr('not that great')); // prints not that great

Result.unwrapOrElse(factory: (err: Err))

Unwraps original value if the result is Ok, otherwise returns value from factory function.

let res = Ok(5);
console.log(res.unwrapOrElse(() => 0)); // prints 5

res = Err('error msg');
console.log(res.unwrapOrElse(() => "not a number")); // prints not a number

Result.expect(message)

Unwraps result or throws new Error with provided message.

let res = Ok(5);
console.log(res.expect('provided message')); // 5

res = Err('error msg');
console.log(res.expect('provided message')); // throws an error: 'provided message'

Result.expectError(message)

Unwraps error from result or throws new Error with provided message.

let res = Ok(5);
console.log(res.expectErr('provided message')); // Exception: provided message

res = Err('error msg');
console.log(res.expectErr('provided message')); // 'error msg'

Result.isOk()

Returns true if result is Ok, otherwise returns false.

let res = Ok(5);
console.log(res.isOk()); // true

res = Err('error msg');
console.log(res.isOk()); // false

Result.isErr()

Returns true if result is Err, otherwise returns false.

let res = Ok(5);
console.log(res.isErr()); // false

res = Err('error msg');
console.log(res.isOk()); // true

Result.ok()

Returns value if result is Ok, or undefined if it's Err.

let res = Ok(5);
console.log(res.ok()); // 5

res = Err('error msg');
console.log(res.ok()); // undefined

Result.err()

Returns error value if result is Err, or undefined if it's Ok.

let res = Ok(5);
console.log(res.err()); // undefined

res = Err('error msg');
console.log(res.err()); // error msg

Result.map(mapper)

Returns new result with mapped value.

const res = Ok(5);
const mappedRes = res.map((val) => val + 1);

console.log(mappedRes.unwrap()); // 6

Result.mapErr(mapper)

Returns new result with mapped error value.

const res = Err('error msg');
const mappedRes = res.mapErr(err => err + ' suffix');
console.log(mappedRes.unwrapErr()); // error msg suffix

Result.mapOrElse(mapper, fallback)

Returns new result with mapped ok value & mapped error value.

const mapOk = (val => val + 1);
const mapErr = (err => err + ' suffix');

console.log(Ok(5).unwrap()) // 6
console.log(Err('error msg').unwrapErr()) // error message suffix

Result.inspect()

Will run provided inspector if result is Ok.

let res = Ok(5);
res.inspect((val) => console.log(val)); // prints 5

res = Err('error msg');
res.inspect((val) => console.log(val)); // prints nothing

Result.inspectErr()

Will run provided inspector if result is Err.

let res = Ok(5);
res.inspect((val) => console.log(val)); // prints noting

res = Err('error msg');
res.inspect((val) => console.log(val)); // prints error msg

Result.toAsync()

Returns new async result constructed from current result.

const res = Ok(5);
const asyncRes = res.toAsync();

Result interface

interface Result<Val, Err> {
    // Contained Promise
    value: Val | Err;

    // Queries
    unwrap(): Val;
    unwrapErr(): Err;
    unwrapOr(altVal: Val): Val;
    unwrapOrElse(altValFactory: (err: Err) => Val): Val;
    expect(msg: string): Val;
    expectErr(msg: string): Err;
    isOk(): this is OK<Val>;
    isErr(): this is ERR<Err>;
    ok(): Val|undefined,
    err(): Err|undefined,

    // Mappers
    map<MappedVal>(mapper: (val: Val) => MappedVal): Result<MappedVal, Err>;
    mapOrElse<MappedVal>(mapper: (val: Val) => MappedVal, fallback: (err: Err) => MappedVal): Result<MappedVal, Err>;
    mapErr<MappedErr>(mapper: (err: Err) => MappedErr): Result<Val, MappedErr>;

    // Utilities
    inspect(inspector: (val: Val) => any): Result<Val, Err>;
    inspectErr(inspector: (err: Err) => any): Result<Val, Err>;
    toAsync(): AsyncResult<Val, Err>;
}

AsyncResult

Class that contains operation result and interaction methods for async code

Static AsyncResult.fromPromise(promise)

Creates async result from promise.

import { AsyncResult } from 'base-ts-result';

const resPromise = AsyncResult.fromPromise(Promise.resolve(1));

Static AsyncResult.fromResult(result)

Creates async result from synchronous result.

import { AsyncResult } from 'base-ts-result';

const resPromise = AsyncResult.fromResult(Ok(5));

Static AsyncResult.fromResultPromise(resultPromise)

Creates async result from result promise.

import { AsyncResult } from 'base-ts-result';

const resPromise = AsyncResult.fromResult(Promise.resolve(Ok(5)));

AsyncResult interface

// Async result implementation for more ergonomic usage of Results with async code
class AsyncResult<Val, Err> {
    // Contained promise
    promise: ResultPromise<Val, Err>; 

    // Creators
    static fromPromise<Val>(promise: Promise<Val>): AsyncResult<Val, unknown>;
    static fromResult<Val, Err>(result: Result<Val, Err>): AsyncResult<Val, Err>;
    static fromResultPromise<Val, Err>(result: ResultPromise<Val, Err>): AsyncResult<Val, Err>;

    // Queries
    async unwrap(): Promise<Val>;
    async unwrapErr(): Promise<Err>;
    async unwrapOr(altVal: Val): Promise<Val>;
    async unwrapOrElse(altValFactory: (err: Err) => AsyncMapped<Val>): Promise<Val>;
    async expect(msg: string): Promise<Val>;
    async expectErr(msg: string): Promise<Err>;
    async isOk(): Promise<boolean>;
    async isErr(): Promise<boolean>;
    async ok(): Promise<Val|undefined>;
    async err(): Promise<Err|undefined>;

    // Mappers
    map<NewVal>(mapper: (val: Val) => AsyncMapped<NewVal>): AsyncResult<NewVal, Err>;

    mapOrElse<NewVal>(
        mapper: (val: Val) => AsyncMapped<NewVal>,
        fallback: (err: Err) => AsyncMapped<NewVal>
    ): AsyncResult<NewVal, Err>;

    mapErr<NewErr>(mapper: (err: Err) => AsyncMapped<NewErr>): AsyncResult<Val, NewErr>;

    // Utilities
    inspect(inspector: (val: Val) => any): AsyncResult<Val, Err>;
    inspectErr(inspector: (err: Err) => any): AsyncResult<Val, Err>;
}

Helpers

toResult(fn)

Converts function return value to result.

import { toResult } from 'base-ts-result';

let res = toResult(() => 2);
console.log(res.unwrap()); // prints 2

res = toResult(() => throw new Err());
console.log(res.unwrapErr()); // prints error

resultify(fn, mapErr)

Wraps the original function with resultifier.

const rawFn = (a: number) => {
    if (a < 0) {
        throw new Error('not today')
    }

    return a;
};

const fn = resultify(
    rawFn,
    err => err.message
);

const res = fn(-2); // Result<number, string>
res.err() // 'not today'

asyncResultify(fn, mapErr)

Converts plain async function to function that return async result.

const rawFn = async (a: number) => {
    if (a < 0) {
        throw new Error('not today')
    }

    return a;
};

const fn = asyncResultify(
    rawFn,
    async err => err.message
); // (a: number) => AsyncResult<number, string>

const res = fn(-2); // AsyncResult<number, string>
await res.err() // 'not today'

createAsyncResult(fn: () => Promise)

Converts function that returns a promise with sync result into function that returns async result.

const resultPromiseFn = async (a: number): ResultPromise<number, string> => {
    await new Promise(() => {
        setTimeOut(() => Promise.resolve(), 100)
    });

    if (a < 0) {
        return Err('err');
    }

    return Ok(a);;
};

// Manual, not convenient way
const valueOne = (await resultPromiseFn(2)).unwrap();

// Using helper
const fn = createAsyncResultFn(resultPromiseFn); // (a: number) => AsyncResult<number, string>
const valueTwo = await fn(2).unwrap(); // Same result, with more convenient async handling

toAsyncResult(promise)

Creates result from a promise.

const promise = Promise.reject();
const result = toAsyncResult(promise);

Sources

• 📦 this package on npm
• this package on github