@aripalo/result

Typesafe error handling (inspired by Go) & data absence protection for TypeScript apps (NodeJS/Browser).

Getting started

Install

npm i @aripalo/result

Example "throwable"

Some irrelevant code for demonstration purposes:

async function randomErrorHelloWorld(): Promise<string> {
  if (Math.random() < 0.5) {
    throw new Error("Random error occurred");
  }
  return "Hello World!";
}

Usage

import { Result } from "@aripalo/result";

const [value, err] = await Result(randomErrorHelloWorld());

if (err) {
  assert(value === null); // true
  assert(err instanceof Error); // true
} else {
  assert(typeof value === "string"); // true
  assert(err === null); // true
}

Purpose

“There are many like it, but this one is mine.”

Writing asynchronous code with async/await looks simple, but once procedural code that depends on the output of previous async steps is being introduced with bit more complex error handling requirements, things start to become complex from control flow perspective.

There are many great alternative solutions to this problem; This one just happens to be the pattern I personally prefer to use.

1. Go-inspired, error as return value

2. Returned error is always an instance of Error

3. Return value (type Maybe) is a Tuple with either value or error present and the other always set to null:

   type Maybe<T> = [value: T, err: null] | [value: null, err: Error];

4. Data absence protection: By default, values that resolve to undefined or null will internally thrown an error, resulting into:

   [value: null, err: Error]

5. Primarily aimed for async functions and Promise objects, but works with synchronous functions too: Anything that is throwable, i.e. "can throw/reject".

6. Works both in NodeJS and Browser environments

Patterns

Receive both

const [value, err] = await Result(randomErrorHelloWorld());

if (err) {
  // handle err, for example return early
  return;
}

// do something with the value

Ignore value

If you're only interested in "did the operation succeed", without caring about the return value:

const [, err] = await Result(randomErrorHelloWorld());

if (err) {
  // handle err
}

Ignore err

When you don't really care if the operation fails, but if it succeeded do something with the return value:

const [value] = await Result(randomErrorHelloWorld());

if (value) {
  // do something with value
}

Disable data absence protection

If your throwable returns/resolves without meaningful data on success, you may specify meaningful: false to prevent the data absence protection:

const [value, err] = await Result(Promise.resolve(undefined), {
  meaningful: false,
});

if (err) {
  // handle err
} else {
  assert(typeof value === "undefined"); // true
}