Discussion on: What's new in ES2022? 🤔

[Rasmus Schultz]

What is error.cause for?

Normally, the cause of the error is what I would put in the error message. I mean, what else would you put there?

Why do we need another field for that?

I don't know of any other language that has two text messages in the same exception. What for? 🤷‍♂️

[Alex Bea]

The error message might sometimes be used for a public-facing message. You could then put more technical information in the cause as well. That's my guess, at least.

[Rasmus Schultz]

That sounds unlikely?

At least, I've never heard of anyone using exceptions for display purposes - exceptions generally do contain technical information, they are usually intended for developers, not for users. How would you deal with localization, for instance... That's just not what exceptions are for...

[Rasmus Schultz]

Ah, mystery solved!

2ality.com/2021/06/error-cause.html

It's for chaining errors - like the "inner exception" you have in many other languages.

Because you can throw anything in JS, the property type isn't specified as Error - but the intention is similar.

[Jasmin Virdi]

Thanks for attaching this link for reference. 🙂

The way this would be super helpful is in deeply nested functions with chained errors.
Like if we have mutiple try catch block inside a deeply nested function so we pass the string as the purpose of that block and cause as the argument of catch block. For example:

function deeplyNested() {
  try {
    // outer block logic.

    let appData = [{...}]
    // app data array parsing.
    appData.map(
      (data) => {
        try {
          // ···
        } catch (error) {
          throw new Error(`While processing ${data}`, {
            cause: error
          });
        }
      });
  } catch (error) {
    throw Error('Error while processing outer block', {
      cause: error
    });
  }
}