fix(ext/timers): some timers are not resolved (#20055)

Fixes https://github.com/denoland/deno/issues/19866

2 files changed, 31 insertions, 1 deletions

diff --git a/cli/tests/unit/timers_test.ts b/cli/tests/unit/timers_test.ts
index c50cb779c..5c076ad09 100644
--- a/cli/tests/unit/timers_test.ts
+++ b/cli/tests/unit/timers_test.ts
@@ -727,3 +727,32 @@ Deno.test({
     assertEquals(output, "");
   },
 });
+
+// Regression test for https://github.com/denoland/deno/issues/19866
+Deno.test({
+  name: "regression for #19866",
+  fn: async () => {
+    const timeoutsFired = [];
+
+    // deno-lint-ignore require-await
+    async function start(n: number) {
+      let i = 0;
+      const intervalId = setInterval(() => {
+        i++;
+        if (i > 2) {
+          clearInterval(intervalId!);
+        }
+        timeoutsFired.push(n);
+      }, 20);
+    }
+
+    for (let n = 0; n < 100; n++) {
+      start(n);
+    }
+
+    // 3s should be plenty of time for all the intervals to fire
+    // but it might still be flaky on CI.
+    await new Promise((resolve) => setTimeout(resolve, 3000));
+    assertEquals(timeoutsFired.length, 300);
+  },
+});
diff --git a/ext/web/02_timers.js b/ext/web/02_timers.js
index cfabdeb98..ade1c7123 100644
--- a/ext/web/02_timers.js
+++ b/ext/web/02_timers.js
@@ -243,6 +243,7 @@ function runAfterTimeout(task, millis, timerInfo) {
     resolved: false,
     prev: scheduledTimers.tail,
     next: null,
+    task,
   };
 
   // Add timerObject to the end of the list.
@@ -286,7 +287,7 @@ function runAfterTimeout(task, millis, timerInfo) {
       while (currentEntry !== null) {
         if (currentEntry.millis <= timerObject.millis) {
           currentEntry.resolved = true;
-          ArrayPrototypePush(timerTasks, task);
+          ArrayPrototypePush(timerTasks, currentEntry.task);
           removeFromScheduledTimers(currentEntry);
 
           if (currentEntry === timerObject) {