Bibek

Posted on Jun 18, 2021 • Originally published at blog.bibekkakati.me

Error Handling in JavaScript (Golang Style)

#javascript #node #webdev #go

In this short article, we are going to see how we can handle error in JavaScript in Golang style.

I am assuming, you have some experience with JavaScript and you are aware of the issues with error handling like throwing an exception to the parent method from try-catch block or chaining multiple then-blocks and implementing logic inside it. These things can easily mess up with the code making it difficult to read.

Golang avoids these type of problems by handling errors/exceptions atomically.

Error handling in Golang



result, err := methodCall()
if err != nil {
  // handle error
}
// do something with the result

We can use a similar pattern in JavaScript with the help of a try-catch block like this.



const getData = async () => {
  try {
    const result = await methodCall();
    return [result, null];
  } catch(error) {
    return [null, error];
  }
}

If any error occurs, we are returning the error in the second position of the array and the result as null in the first position.

If there is no error, we are returning the result in the first position and error as null in the second position.

Now we can call the getData method then handle the result and error like this.



const [result, error] = await getData();
if (error !== null) {
  // handle the error
}
// do something with the result

This pattern of error handling makes it very easy to read and understand the code.

Let me know what do you think about this pattern.

Originally published on blog.bibekkakati.me

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Top comments (31)

Drumstickz64 • Jun 19 '21 • Edited

You can actually turn this into a utility function, like so:

async function goCatch(promise) {
    try {
        const result = await promise
        return [result, null]
    } catch (err) {
        return [null, err]
    }
}

You could also use an object like Brendan said.

𒎏Wii 🏳️‍⚧️ • Jun 19 '21

I would wrap it in a higher order function though, something that takes an async function and returns a new async function with the added catch logic

𒎏Wii 🏳️‍⚧️ • Jun 21 '21 • Edited

Something like this, I guess:

const safe = fn => (*args) => fn(*args)
   .then(res => [res, null])
   .catch(err => [null, err])

Bibek • Jun 19 '21

Yeah. That can be way of implementing it.

Bibek • Jun 19 '21 • Edited

Yeah. Utility function can be very helpful.

DouglasCalora • Jun 19 '21 • Edited

import { Loading, Notify } from 'quasar'

/**
 * @param {Promise} promise
 * @param {object} config={notifySuccess, notifyError, useLoading}
 * @example promiseHandle(new Promise(), { notifyError: { message: 'Erro' }, notifySuccess: { message: 'Sucesso' } })
 */
export default async function (promise, config = {}) {
  const {
    notifySuccess = {},
    notifyError = {},
    useLoading = false,
    onLoading
  } = config

  onLoading && onLoading(true)
  useLoading && Loading.show()

  const primiseToBeExec = typeof promise === 'function' ? promise() : promise
  const hasNotify = notify => Object.keys(notify).length

  try {
    const data = await (Array.isArray(promise) ? Promise.all(promise) : primiseToBeExec)
    hasNotify(notifySuccess) && Notify.create({ type: 'success', ...notifySuccess })
    return { data, error: null }
  } catch (error) {
    hasNotify(notifyError) && Notify.create({ type: 'error', ...notifyError })
    return { data: null, error }
  } finally {
    onLoading && onLoading(false)
    Loading.hide()
  }
}

I added a callback onLoading so I can do somenthing while function is running.

const { data, error } = await promiseHandler(callbackFn, { onLoading: value => console.log('is loading?', value) })

Bibek • Jun 20 '21

👨🏼‍💻

Calin Baenen • Jun 20 '21

Better yet, just use GoLang.

Bibek • Jun 20 '21

Good idea. 😉

Calin Baenen • Jun 20 '21 • Edited

~~Of course it is! Everyone knows Go is the best language objectively.~~

Calin Baenen • Jul 17

I've reconsidered. . .

Calin Baenen • Jul 17

Thinking back, I spoke very unwise words.
It should be "Better yet, just use Rust." — Rust's error handling is exceptional. :þ

Brendan Mullins • Jun 18 '21

Nice, but I would personally use an object instead of the array as a return type

Bibek • Jun 19 '21

I prefer array because if we use object, destructuring will be an issue if there is more than one block in same level. Also we need to be aware of the property name.

Jan Küster • Jun 19 '21

Property name can be set by convention across your whole project. Let's say { error, result } which is to me most verbose and would not lead to accidental access compared to array indices

Bibek • Jun 19 '21

Yeah, that is right. But in case of multiple blocks in the same scope it can create issue, as you will not be able de-structure it like this

const {error, result} = await method();

// second method call will create an issue
const {error, result} = await method2();

But in case of array, you can use other variable name in the second method call.

Feel free to correct me, if I am missing something.

Brendan Mullins • Jun 19 '21

a few ways you could avoid this:

const responseOne = await methodOne();
if (responseOne.error) return

const responseTwo = await methodTwo();
if (responseTwo.error) return

// of if you want destructuring
const {error: methodOneError, result: resultOne} = await methodOne();
if (methodOneError) return
const {error: methodTwoError, result: restultTwo} = await methodTwo();
if (methodTwoError) return

Im not saying the array descructuring is worse, its just a prefference

Erik Hofer • Jun 19 '21

You can rename the variable when destructuring an object.

const {error, result} = await method();

const {error: error2, result: result2} = await method2();

Bibek • Jun 19 '21

@jsnanigans Yeah, It's just a preference.

Bibek • Jun 19 '21 • Edited

@erikhofer I am aware of that.

Grzegorz Bielski • Jun 20 '21

I'm not a huge fan of this pattern.
The idea of explicitly returning errors rather than throwing unchecked errors is great, but the proposed implementation is flawed - we need to always check the elements of the tuple before using the value to see if there is an error which will become error-prone rather quickly.
Fortunately, this is an already solved problem, known in other langues as Either or Result type, in which all of these ifs are abstracted away in form of map and flatMap / chain operations.
Potential implementation: gigobyte.github.io/purify/adts/Eit...

Bibek • Jun 20 '21

Got your point. After all it's all about own preference.

Chinmay Kabi • Jun 19 '21

I saw this in a Fireship video, ditto 👀

Bibek • Jun 19 '21

Is it? Need to check it.

I saw this in a 3 years old article.

njavilas2015 • Sep 4 '22 • Edited

in typescript

async function goCatch<T>(promise: Promise<T>): Promise<[T | null, null | Error]> {
    try {

        const result: Awaited<T> = await promise

        return [result, null]

    } catch (err) { return [null, err] }
}


const main = async (params: params) => {


    const [store, err] = await goCatch(qbpbspfzfeyudz.create(params.store))

}