What is the recommanded what to turn Javascript callback bas

Question

What is the recommanded what to turn Javascript callback based API like `EventSource` to a `Flow` that emits the data received by the `onmessage` callback

sdeleuze · Answer

My original code is ``` window onload = EventSource message stream onmessage = val message = JSON parse lt Message gt it data as String val li = document createElement li apply innerHTML = Message $ message content from user $ message user document getElementById messages appendChild li Unit Ugly workaround for <https youtrack jetbrains com issue KT 22635> ```

sdeleuze · Answer

I would like to extract the `EventSource message stream onmessage` to something that provides a `Flow lt String gt `

sdeleuze · Answer

I will then use operators to turn it to `Message` and do whatever is needed with the DOM

sdeleuze · Answer

I tried ``` fun EventSource asFlow = flow onmessage = emit JSON parse lt Message gt it data as String Unit ``` But it does not work since `onmessage` is not suspending

Vsevolod Tolstopyatov [JB] · Answer

Currently the only way is to use `callbackFlow` `channelFlow` one is alias to another the only difference is your intention But you have to manage backpressure somehow drop messages when `channel offer` returns `false` use conflated or unlimited channel

Vsevolod Tolstopyatov [JB] · Answer

In the future we will provide StateFlow DataFlow that are similar to Rx subjects Reactor processors

sdeleuze · Answer

Make sense thanks for your feedback

sdeleuze · Answer

It is maybe too early but providing extensions like `EventSource asFlow ` out of the box would increase significantly Kotlin added value for frontend developement

Vsevolod Tolstopyatov [JB] · Answer

sdeleuze · Answer

Thanks I will make a complete feedback after my Devoxx deepdive

Vsevolod Tolstopyatov [JB] · Answer

it would be very helpful

sdeleuze · Answer

I am pretty amazed by 2 things The awesomeness of Coroutines 1 3 on frontend The lack of up to date documentation and samples given all the changes on Gradle + multiplatform + Kotlin JS

sdeleuze · Answer

So the potential is huge

sdeleuze · Answer

But at some point IMO you will need to pause the features and just make documentation up to date provide samples and make multiplatform Gradle config more approachable

sdeleuze · Answer

But great stuff congrats to the team

sdeleuze · Answer

Another similatr question for single value callback I saw <https stackoverflow com questions 48552925 existing 3 function callback to kotlin coroutines 48562175 48562175> but when I try to use it for `window onload` I get compile time errors ``` suspend fun Window awaitLoad = suspendCoroutine lt Unit gt cont gt onload = cont resume Unit ```

sdeleuze · Answer

I get `Methods are absent in coroutines classes since 1 3`

sdeleuze · Answer

Oh I used the wrong one

sdeleuze · Answer

It works with `import kotlin coroutines suspendCoroutine`