ts-results

ts-results

A typescript implementation of Rust's Result object.

Installation

$ npm install ts-results

or

$ yarn install ts-results

Usage

import { Result, Err, Ok, Results } 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 = Ok<number, Error>(1);
let badResult = Err<number, Error>(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

let goodResult = Ok<number, Error>(1);
let badResult = Err<number, Error>(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, err => new Error('mapped')).unwrap(); // 2
badResult.map(num => num + 1, err => new Error('mapped')).unwrap(); // throws Error("mapped")

goodResult.map(null, err => new Error('mapped')).unwrap(); // 1
badResult.map(null, err => new Error('mapped')).unwrap(); // throws Error("mapped")

Else

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

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

Combining Results

There may be some cases where we have two or more separate Result objects and we want to do something with both values. This is handled by using the Results function to combine them.

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

let result = Results(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.