2021-09-15
5223
#vanilla javascript
James Sinclair
270
Sep 15, 2021 ⋅ 18 min read

Using the JavaScript Either monad for error handling

James Sinclair I am passionate about functional programming, test-driven development, and continuous delivery. I am also interested in neural networks and deep learning.

Recent posts:

DesignCoder and the future of AI-generated UI

From sketches to code in minutes, DesignCoder shows how AI-generated, hierarchy-aware UIs could change the way developers prototype and ship apps.

Rosario De Chiara
Oct 7, 2025 ⋅ 5 min read

Would You Use If() functions in CSS?

It’s 2025, and CSS finally thinks logically. The if() function brings real conditional styling — no hacks, no JS workarounds. Here’s how to use it right.

Ikeh Akinyemi
Oct 7, 2025 ⋅ 16 min read
Typescript or Zod for Validation?

TypeScript vs Zod: Clearing up validation confusion

Learn when to use TypeScript, Zod, or both for data validation. Avoid redundant checks and build safer, type-sound applications.

Alexander Godwin
Oct 6, 2025 ⋅ 3 min read
Wasm 3 Before GTA 6 LogRocket Article

We got Wasm 3.0 before GTA 6: Meet the web’s new engine

Discover how WebAssembly 3.0’s garbage collector, exception handling, and Memory64 transform Wasm into a true mainstream web platform.

Ikeh Akinyemi
Oct 3, 2025 ⋅ 2 min read
View all posts

5 Replies to "Using the JavaScript Either monad for error handling"

  1. Honestly I don’t like this approach for handling errors/exceptions, for me it’s better to read this:

    async function read(id, db) {
    let category = null;

    try {
    category = await db.models.Category.findByPk(id);
    } catch (error) {
    return { success: false, data: null, error: error };
    }

    return { success: true, data: category, error: null };
    }

    router.get(‘categories/:id’, function (req, res, next) {
    let result = await read(req.params.id);
    if (result.success) {
    next(result.error);
    } else {
    res.json(result.data);
    }
    });

    Here I’m handling the possible exceptions successfully, the function will always return a value that’s an object with the flag of “success” as true or false to later do the proper work using the data or the error object.

    I see a better error handling there using a procedural style than trying to figure out what a external dependency that have a flat, left, Ap, right, either, chain etc functions will do for me, I don’t see the intentions of the code clearly, in the procedural way I see the solution easy.

    1. Hi James, thanks for pointing that out. I’ve fixed the formatting for the `Left` and `Right` blocks and have done a bit of extra cleanup as well. Cheers

Leave a Reply