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Fix JS feature detection so that it no longer crashes #2188

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Fix JS feature detection so that it no longer crashes #2188

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17 changes: 11 additions & 6 deletions core/js/src/main/scala/cats/effect/unsafe/PolyfillExecutionContext.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -25,25 +25,30 @@ import scala.util.Random
* Based on https://github.com/YuzuJS/setImmediate
*/
private[unsafe] object PolyfillExecutionContext extends ExecutionContext {
private[this] val Undefined = "undefined"

def execute(runnable: Runnable): Unit =
setImmediate(() => runnable.run())

def reportFailure(cause: Throwable): Unit =
cause.printStackTrace()

private[this] def isAvailable(a: => js.Dynamic): Boolean =
try {
a.asInstanceOf[js.UndefOr[Any]].isDefined
} catch {
case _: Throwable => false
}
Comment on lines +35 to +40
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How about !js.isUndefined(a)? Is that the same?

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I think I tried this when I implemented the web worker polyfill and ran into problems, but maybe I did it wrong.

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No js.isUndefined wouldn't work because it only tests whether a strict/eager value is undefined or not, but the problem is an exception is being thrown when attempting to resolve that value. Personally I think it's silly behaviour but sjrd is very, very adamant in these things. It is what it is now so when testing for optional JS features we need to always be ready to catch a (Fatal) exception.

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Awesome, good to know. Thanks.


private[this] val setImmediate: (() => Unit) => Unit = {
if (js.typeOf(js.Dynamic.global.setImmediate) == Undefined) {
if (!isAvailable(js.Dynamic.global.setImmediate)) {
var nextHandle = 1
val tasksByHandle = mutable.Map[Int, () => Unit]()
var currentlyRunningATask = false

def canUsePostMessage(): Boolean = {
// The test against `importScripts` prevents this implementation from being installed inside a web worker,
// where `global.postMessage` means something completely different and can't be used for this purpose.
if (js.typeOf(js.Dynamic.global.postMessage) != Undefined && js.typeOf(
js.Dynamic.global.importScripts) == Undefined) {
if (isAvailable(js.Dynamic.global.postMessage) && !isAvailable(js.Dynamic.global.importScripts)) {
var postMessageIsAsynchronous = true
val oldOnMessage = js.Dynamic.global.onmessage

Expand Down Expand Up @@ -99,7 +104,7 @@ private[unsafe] object PolyfillExecutionContext extends ExecutionContext {
}
}

if (js.typeOf(js.Dynamic.global.addEventListener) != Undefined) {
if (isAvailable(js.Dynamic.global.addEventListener)) {
js.Dynamic.global.addEventListener("message", onGlobalMessage _, false)
} else {
js.Dynamic.global.attachEvent("onmessage", onGlobalMessage _)
Expand All @@ -113,7 +118,7 @@ private[unsafe] object PolyfillExecutionContext extends ExecutionContext {
js.Dynamic.global.postMessage(messagePrefix + handle, "*")
()
}
} else if (js.typeOf(js.Dynamic.global.MessageChannel) != Undefined) {
} else if (isAvailable(js.Dynamic.global.MessageChannel)) {
val channel = js.Dynamic.newInstance(js.Dynamic.global.MessageChannel)()

channel.port1.onmessage = { (event: js.Dynamic) =>
Expand Down