use Object instead of Map for promise table (#4309)

1 files changed, 7 insertions, 4 deletions

diff --git a/cli/js/ops/dispatch_json.ts b/cli/js/ops/dispatch_json.ts
index 6fb9007df..4aa1f6b8b 100644
--- a/cli/js/ops/dispatch_json.ts
+++ b/cli/js/ops/dispatch_json.ts
@@ -19,7 +19,10 @@ interface JsonResponse {
   promiseId?: number; // Only present in async messages.
 }
 
-const promiseTable = new Map<number, util.Resolvable<JsonResponse>>();
+// Using an object without a prototype because `Map` was causing GC problems.
+const promiseTable: {
+  [key: number]: util.Resolvable<JsonResponse>;
+} = Object.create(null);
 let _nextPromiseId = 1;
 
 function nextPromiseId(): number {
@@ -48,9 +51,9 @@ export function asyncMsgFromRust(resUi8: Uint8Array): void {
   const res = decode(resUi8);
   util.assert(res.promiseId != null);
 
-  const promise = promiseTable.get(res.promiseId!);
+  const promise = promiseTable[res.promiseId!];
   util.assert(promise != null);
-  promiseTable.delete(res.promiseId!);
+  delete promiseTable[res.promiseId!];
   promise.resolve(res);
 }
 
@@ -89,7 +92,7 @@ export async function sendAsync(
     promise.resolve(res);
   } else {
     // Async result.
-    promiseTable.set(promiseId, promise);
+    promiseTable[promiseId] = promise;
   }
 
   const res = await promise;