Question about onStart execution order

In the following example I was expecting “onStart” callback to be invoked first, but noticed it was run last:

https://codepen.io/ejez/pen/NWjWBoJ

const src = fromArray([0, 1]);

const { unsubscribe } = pipe(
  src,

  onStart(() => console.log("onStart...")),

  onPush(() => console.log("onPush...")),

  onEnd(() => console.log("onEnd...")),

  subscribe((result) => console.log(result))
);

result:

"onPush..."
0
"onPush..."
1
"onEnd..."
"onStart..."

From the docs:

When the stream starts then the sink is called with Start, Then for every incoming, new value it’s called with Push('a), and when the stream ends it’s finally called with End.

onStart Run a callback when the Start signal is sent to the sink by the source.

Many thanks.

[ejez]

Thanks!

What i did, is adding a condition for setting fetching to true in onSart (only when there is no data, ie first fetch). I will change it as per your suggestion, as it seems onStart is not the natural place for setting the fetching state.

[kitten]

yea, sounds good 👍 I’ll close this for now, since I think the question itself is addressed.

The problems here and ambition is basically always with synchronous streams. The synchronous support in Wonka allows us to apply some nice tricks in urql, but that does come with some caveats. Synchronous events are just very different from asynchronous as it’ll always deal with an exact order.