Use ordinary JS object instead of Scala Map

Author: armanbilge

core/src/main/scala/org/scalajs/macrotaskexecutor/MacrotaskExecutor.scala

@@ -16,9 +16,9 @@
 
 package org.scalajs.macrotaskexecutor
 
-import scala.collection.mutable
 import scala.concurrent.{ExecutionContext, ExecutionContextExecutor}
 import scala.scalajs.js
+import scala.scalajs.js.annotation._
 import scala.util.Random
 import scala.util.control.NonFatal
 
@@ -34,10 +34,18 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
   def reportFailure(cause: Throwable): Unit =
     cause.printStackTrace()
 
+  @js.native
+  private[this] trait TaskMap extends js.Object {
+    @JSBracketAccess
+    def apply(handle: Int): Runnable
+    @JSBracketAccess
+    def update(handle: Int, task: Runnable): Unit
+  }
+
   private[this] val setImmediate: Runnable => Unit = {
     if (js.typeOf(js.Dynamic.global.setImmediate) == Undefined) {
       var nextHandle = 1
-      val tasksByHandle = mutable.Map[Int, Runnable]()
+      val tasksByHandle = (new js.Object).asInstanceOf[TaskMap]
       var currentlyRunningATask = false
 
       def canUsePostMessage(): Boolean = {
@@ -67,17 +75,15 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
         if (currentlyRunningATask) {
           js.Dynamic.global.setTimeout(() => runIfPresent(handle), 0)
         } else {
-          tasksByHandle.get(handle) match {
-            case Some(task) =>
-              currentlyRunningATask = true
-              try {
-                task.run()
-              } finally {
-                tasksByHandle -= handle
-                currentlyRunningATask = false
-              }
-
-            case None =>
+          val task = tasksByHandle(handle)
+          if (!js.isUndefined(task)) {
+            currentlyRunningATask = true
+            try {
+              task.asInstanceOf[Runnable].run()
+            } finally {
+              js.special.delete(tasksByHandle, handle)
+              currentlyRunningATask = false
+            }
           }
         }
 
@@ -129,7 +135,7 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
           val handle = nextHandle
           nextHandle += 1
 
-          tasksByHandle += (handle -> k)
+          tasksByHandle(handle) = k
           js.Dynamic.global.postMessage(messagePrefix + handle, "*")
           ()
         }
@@ -144,7 +150,7 @@ object MacrotaskExecutor extends ExecutionContextExecutor {
           val handle = nextHandle
           nextHandle += 1
 
-          tasksByHandle += (handle -> k)
+          tasksByHandle(handle) = k
           channel.port2.postMessage(handle)
           ()
         }