Why does `Observable.prototype.subscribe` report thrown errors from `observer.start(sub)` asynchronously instead of just propagating them?

tc39 / proposal-observable

Observables for ECMAScript

https://tc39.github.io/proposal-observable/

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Why does `Observable.prototype.subscribe` report thrown errors from `observer.start(sub)` asynchronously instead of just propagating them? #195

Open dead-claudia opened 6 years ago

dead-claudia commented 6 years ago

In steps 7-9, it always calls HostReportError, despite it being clearly within the JS call stack. Is there a reason this is the case, in contrast with the rest of the spec?