@barndev/result

Typescript errors-as-values implementation with opt-in runtime enum.

@barndev/result exports a single type, Result which can have either a data: T or an error: string | Error, but never both. The alternate @barndev/result/enum entrypoint exports an enum-like object that can be used at runtime to create Results.

Installation

If runtime enum is not used, @barndev/result can be installed as a dev dependency.

Type only

npm i -D @barndev/result

Runtime enum

npm i @barndev/result

/enum entrypoint can also be imported directly from esm.sh CDN.

import { Result } from 'https://esm.sh/@barndev/result/enum';

Usage

Creating a Result

Result should be used anywhere an error can occur.

Type only

import type { Result } from '@barndev/result';

async function readConfig(): Promise<Result<Config>> {
    try {
        const json = await readFile('config.json');
        const config = JSON.parse(json);
        return { data: config, error: null };
    } catch (err) {
        console.error(err);
        return {
            data: null,
            error: `Failed to read config. Error ${err}`,
        };
    }
}

Runtime enum

import { Result } from '@barndev/result/enum';

async function fetchPosts(): Promise<Result<Post[]>> {
    try {
        const res = await (await fetch('/posts')).json();
        return Result.Ok(res.posts);
    } catch (err) {
        console.error(err);
        return Result.Err(`Failed to fetch posts. Error: ${err}`);
    }
}

Handling a Result

Guard clauses with early returns can be used to take advantage of type narrowing.

function handleResult(res: Result<string>) {
    if (res.error !== null) {
        doErrorStuff(res.error);
        //               ^? error: string | Error
        return;
    }
    doSuccessStuff(res.data);
    //                 ^? data: string
}