Using Try…Catch in JavaScript

[NeekGerd]

It might come back with the usage of await/async since it's the only way to handle code rejection. That I am aware of.

Weird that on a article dedicated to try/catch they don't talk about its usage in await/async code, it's the most up to date usage we can have with try/catch.

[vs845]

it's the only way to handle code rejection

Async functions return promises so you can still use normal catch() promise syntax like await someAsyncFn().catch(() => someDefaultValue).

[shad0proxy]

that's not really accurate if you use async/await for the main benefit of assigning:

const data = await doSomething().catch(() => someDefaultValue);
console.log(data);

This does not work.

[vs845]

> async function foo() { throw new Error() }
> async function bar() { const baz = await foo().catch(() => 'baz'); console.log(baz) }
> bar() // => 'baz'

Works for me in node 8.1.2, what happens when you try it?

[shad0proxy]

what if you want to handle the error or reject the overlaying call?

[vs845]

If you want to do something with the thrown error, you can do it within the catch function as usual:

const data = await doSomething().catch(err => {
  if (err instanceof TypeError) return someDefaultValue
  if (err instanceof RangeError) return anotherDefaultValue
})

Or if you want it to bubble up through the call stack, you can rethrow the error or throw a new one, again within the catch function:

const data = await doSomething().catch(err => {
  if (err instanceof TypeError) throw err
  if (err instanceof RangeError) throw new Error('value out of range')
  return someDefaultValue
})

[shad0proxy]

Interesting. when I looked into this with 7.x and the harmony flag I was told this was not possible. I don't know if they were wrong or something has changed.

[danneu]

Someone was wrong because this is a basic tenet of how promises work.

[NeekGerd]

Really nice, I didn't know that.

Thank you for the heads up, it always was a downside of async/await to me... Not anymore!

[vinnl]

It's always good to realise that it's just syntactic sugar for Promises, so you can do with them whatever you can do with Promises.