I added JS target to my KMP project and now suddenly I cannot use `<http://Dispatchers.IO|Dispatcher...

# multiplatform

[Vaibhav Jaiswal]

I added JS target to my KMP project and now suddenly I cannot use <http://Dispatchers.IO|Dispatchers.IO> in commonMain
It was there when the project only targeting android and iOS and not js(IR)

[Michael Krussel]

You can only use functions and properties in commonMain that are available on all the targets you are using. JS does not have a <http://Dispatcher.IO|Dispatcher.IO> so you cannot use it.

Instead you will have to create some expect function or property that will return the dispatcher you want to use for IO.

[Vaibhav Jaiswal]

Which dispatcher to use for JS?

[Michael Krussel]

Would be a nice things for Kotlin to just include by default, even if JS returns the same dispatcher for every value in Dispatchers.

[Michael Krussel]

I haven't used JS, but I think they only have one since they don't support threads.

[Michael Krussel]

I would probably go with Default, it's the closest to IO.

[Vaibhav Jaiswal]

Thanks,
even runBlocking is not in JS

[Michael Krussel]

yep

[Vaibhav Jaiswal]

Any idea on how runBlocking can be achieved on JS side?

[Michael Krussel]

There's been a lot of discussion on it in the past, but you could look at how runTest is implemented in JS.

[Vaibhav Jaiswal]

runTest is not in JS

[Michael Krussel]

I thought it was, but I've never used js

[Vaibhav Jaiswal]

No issues, thanks for helping

[Michael Krussel]

This imp[lies that it is available

On JVM and Native, this function behaves similarly to runBlocking, with the difference that the code that it runs will skip delays. This allows to use delay in tests without causing them to take more time than necessary. On JS, this function creates a Promise that executes the test body with the delay-skipping behavior.

https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-test/kotlinx.coroutines.test/run-test.html

[Vaibhav Jaiswal]

My use case is a bit different

expect fun <T> runBlocking(
    context: CoroutineContext = EmptyCoroutineContext, 
    block: suspend CoroutineScope.() -> T
): T

This returns the data of type T which is what I want
I tried using GlobalScope, but it returns a Job or a Deferred

[Michael Krussel]

I think if you are going to support JS you will need to be able to wait for the answer in a non blocking manner. Since there is only one thread in JavaScript, you cannot block that thread.