Xstate: Resolving promise within invoke triggers onError

[bradwoods]

Bug

Description:

When using a promise as the value of src within invoke, if the promise resolves, onError is triggered.

Expected result:

onSuccess triggered

Actual result:

onError triggered

Potential fix:

Uncomment function fromPromise in xstate/src/invoke.ts

[davidkpiano]

Do you have a reproducible code example?

[bradwoods]

sure, codesandbox

[davidkpiano]

Funny enough, this is working as intended because there is an error ❌:

If you log out the event data from the error:

        onError: {
          target: "failure",
          actions: (_, e) => console.error(e.data)
        }

You will see:

Error: Child state 'success' does not exist on 'user'

And that's exactly what happened - you don't have a success state. Add it and it works 👍

---

I'm going to keep this open because I want to better handle what happens if you _don't_ have an onError handler and an error occurs anyway (the script should throw that exact error).

[bradwoods]

That makes sense. I may have messed up the example when moving it to code sandbox but the source of the problem I had was using the property onSuccess instead of onDone, which logs out this error: Machine 'user' does not accept event 'done.invoke.promise'. Not sure where I picked up the onSuccess property, I see in the docs example it is onDone.

[bradwoods]

I also made the assumption thatonDone was synonymous with the JS promise method .finally, which triggers after success or error.

[davidkpiano]

The names onDone and onError come from the SCXML Spec, which raises:

• done.invoke.<id> when the invoked service has reached its final state
• error.execution when errors occur during execution

In fact, you don't even need to use onDone and onError - these are just sugar for those SCXML event names:

{
  on: {
    'done.invoke.someID': 'success',
    'error.execution': {
      target: 'failure',
      cond: (ctx, e) => e.src === 'someID'
    }
  }
}

[bradwoods]

Interesting, the onDone & onError syntax is quite nice though.

[davidkpiano]

Should be fixed in master thanks to @jjkola's work.