[K/JS] Export Channel interface itself as well as SendChannel and Rec…

buildSrc/src/main/kotlin/kotlin-shared-conventions.gradle.kts

@@ -16,6 +16,7 @@ private fun KotlinCommonCompilerOptions.configureGlobalKotlinArgumentsAndOptIns(
     optIn.addAll(
         "kotlin.experimental.ExperimentalTypeInference",
         "kotlin.js.ExperimentalJsExport",
+        "kotlin.js.ExperimentalJsStatic",
         // our own opt-ins that we don't want to bother with in our own code:
         "kotlinx.coroutines.DelicateCoroutinesApi",
         "kotlinx.coroutines.ExperimentalCoroutinesApi",

kotlinx-coroutines-core/common/src/channels/BufferOverflow.kt

@@ -1,5 +1,7 @@
 package kotlinx.coroutines.channels
 
+import kotlinx.coroutines.internal.JsOptionalExport
+
 /**
  * A strategy for buffer overflow handling in [channels][Channel] and [flows][kotlinx.coroutines.flow.Flow] that
  * controls what is going to be sacrificed on buffer overflow:
@@ -11,6 +13,7 @@ package kotlinx.coroutines.channels
  * - [DROP_LATEST] — the buffer remains unchanged on overflow, and the value that we were going to add
  *   gets discarded, all without suspending.
  */
+@JsOptionalExport(couldBeConvertedToExplicitExport = true)
 public enum class BufferOverflow {
     /**
      * Suspend until free space appears in the buffer.

kotlinx-coroutines-core/common/src/channels/Channel.common.kt

@@ -1274,6 +1274,8 @@ public interface ChannelIterator<out E> {
  * > Note that if any work happens between `openResource()` and `channel.send(...)`,
  * > it is your responsibility to ensure that resource gets closed in case this additional code fails.
  */
+
+@JsOptionalExport(couldBeConvertedToExplicitExport = true)
 public interface Channel<E> : SendChannel<E>, ReceiveChannel<E> {
     /**
      * Constants for the channel factory function `Channel()`.
@@ -1413,6 +1415,34 @@ public interface Channel<E> : SendChannel<E>, ReceiveChannel<E> {
         internal val CHANNEL_DEFAULT_CAPACITY = systemProp(DEFAULT_BUFFER_PROPERTY_NAME,
             64, 1, UNLIMITED - 1
         )
+
+        /**
+         * Creates a new [Channel] for JavaScript/TypeScript interop.
+         *
+         * This factory is intended for JS export scenarios that rely on `@JsOptionalExport`.
+         * It allows creating channels from JavaScript only when [Channel] is reachable through
+         * an exported declaration signature, instead of unconditionally exporting the top-level
+         * `Channel(...)` factory.
+         *
+         * This helps avoid keeping extra JS-exported API surface when it is not used.
+         *
+         * Behavior is equivalent to:
+         * `Channel(capacity, onBufferOverflow, onUndeliveredElement)`.
+         *
+         * @param capacity Channel buffer capacity. Defaults to [RENDEZVOUS].
+         * @param onBufferOverflow Buffer overflow strategy. Defaults to [BufferOverflow.SUSPEND].
+         * @param onUndeliveredElement Optional callback invoked for each element that was sent
+         * but could not be delivered to a receiver.
+         *
+         * @return A newly created [Channel] instance.
+         */
+        @JsStatic
+        @Suppress("NOTHING_TO_INLINE")
+        public inline fun <E> of(
+            capacity: Int = RENDEZVOUS,
+            onBufferOverflow: BufferOverflow = BufferOverflow.SUSPEND,
+            noinline onUndeliveredElement: ((E) -> Unit)? = null
+        ): Channel<E> = Channel(capacity, onBufferOverflow, onUndeliveredElement)
     }
 }