in JS you can turn any callback into an async () =...

# javascript

[Bernhard]

in JS you can turn any callback into an async () => { } callback and await stuff in it; how do you do that in Kotlin

[turansky]

suspend functions, lambdas

[Bernhard]

how would that look with lambdas?

[Bernhard]

like a function in this shape: func("param") { }

[turansky]

fun func(
    p: String,
    block: suspend () -> Unit,
) {
    // your code
}

[Bernhard]

my function definition is provided by a framework and just takes a normal function

[Bernhard]

I don't think you can do something like: func("param") suspend { }

[turansky]

async function = function, which returns Promise - no magic

[Bernhard]

right, but I want to use an await() in there

[Bernhard]

func("param") { 
    fetch("url").await()
}

[Bernhard]

you can do that as well in js and just work with .then() chains; but you can just plaster an async before the lambda to be able to use await:

func("param", async () => { await fetch("url") })

[turansky]

func("param") {
    GlobalScope.promise { 
        fetch("url")
    }
}

[Bernhard]

ok, so basically something similar to GlobalScope.launch in there

[Bernhard]

does that simply turn a GlobalScope.launch into a Promise type?

[Bernhard]

ah and open an async block

[Bernhard]

thank you!

[turansky]

JFYI

[Bernhard]

looks like you'll need GlobalScope a ton in JS; do you just ignore the warnings?

[Bernhard]

or put @OptIn(DelicateCoroutinesApi::class) everywhere

[turansky]

We use following construction

[turansky]

You can create custom promise factory like this:

fun <T> buildPromise(
    block: suspend () -> T,
): Promise<T> = 
    CoroutineScope(EmptyCoroutineContext).promise(block = block)

[turansky]

To avoid duplication

[Bernhard]

thanks, so the EmptyCoroutineContext sort of gets translated nicely to JS in this case

[Bernhard]

thank you for your continued help 🙂

[turansky]

async lambda in JS will give you isolated error context.
Similar task in Kotlin can be solved with isolated coroutine scope (not global).
I personally don't have use cases for GlobalScope