From 9975bd23cdba7e196ca97c3fcec41a6eee925e57 Mon Sep 17 00:00:00 2001
From: Rudy Mizrahi Celekli <47457359+rudycelekli@users.noreply.github.com>
Date: Mon, 5 Oct 2026 03:02:47 -0400
Subject: [PATCH] fix(replay): preserve Date call and explicit constructor
 semantics (#512)

Signed-off-by: RudyCelekli <47457359+rudycelekli@users.noreply.github.com>
Co-authored-by: morluto <76467478+morluto@users.noreply.github.com>
---
 src/replay/JavaScriptReplayWorker.ts          | 16 +++++++--
 .../replay/javascriptReplayWorker.test.ts     | 35 +++++++++++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)

diff --git a/src/replay/JavaScriptReplayWorker.ts b/src/replay/JavaScriptReplayWorker.ts
index 2af759e8d..900f78f90 100644
--- a/src/replay/JavaScriptReplayWorker.ts
+++ b/src/replay/JavaScriptReplayWorker.ts
@@ -276,8 +276,13 @@ const deterministicContext = (request: WorkerRequest, caseIndex: number) => {
   };
   const epoch = Date.parse(request.determinism.clockIso);
   class ReplayDate extends Date {
-    constructor(...arguments_: [] | [string | number]) {
-      super(arguments_.length === 0 ? epoch : arguments_[0]);
+    constructor(...arguments_: unknown[]) {
+      super(epoch);
+      if (arguments_.length > 0) {
+        const date: unknown = Reflect.construct(Date, arguments_, new.target);
+        if (!types.isDate(date)) throw new TypeError("Invalid Date instance");
+        return date;
+      }
     }
     static override now(): number {
       return epoch;
@@ -286,7 +291,12 @@ const deterministicContext = (request: WorkerRequest, caseIndex: number) => {
   const replayMath: Math = Object.create(Math);
   Object.defineProperty(replayMath, "random", { value: random });
   return createContext(
-    { Date: ReplayDate, Math: replayMath },
+    {
+      Date: new Proxy(ReplayDate, {
+        apply: () => new ReplayDate().toString(),
+      }),
+      Math: replayMath,
+    },
     {
       name: "rea-controlled-replay",
       codeGeneration: { strings: false, wasm: false },
diff --git a/tests/boundary/providers/replay/javascriptReplayWorker.test.ts b/tests/boundary/providers/replay/javascriptReplayWorker.test.ts
index dce65a6d3..c74ef282e 100644
--- a/tests/boundary/providers/replay/javascriptReplayWorker.test.ts
+++ b/tests/boundary/providers/replay/javascriptReplayWorker.test.ts
@@ -226,6 +226,41 @@ describe("disposable JavaScript replay worker", () => {
   });
 });
 
+describe("deterministic replay Date compatibility", () => {
+  it.each([
+    ["new Date(2020, 0, 2).getFullYear()", 2020],
+    ["new Date(2020, 0, 2, 3, 4, 5, 6).getMilliseconds()", 6],
+    ["typeof Date()", "string"],
+    ["Date() === new Date().toString()", true],
+    ["new Date().toISOString()", "2000-01-01T00:00:00.000Z"],
+    ["Date.now()", 946684800000],
+    ["new Date(0).getTime()", 0],
+    [
+      "new Date('2020-01-02T00:00:00Z').toISOString()",
+      "2020-01-02T00:00:00.000Z",
+    ],
+    ["new Date() instanceof Date", true],
+    [
+      "(() => { class ChildDate extends Date {} const date = new ChildDate(2020, 0, 2); return [date instanceof ChildDate, date instanceof Date, date.getFullYear(), date.constructor === ChildDate]; })()",
+      [true, true, 2020, true],
+    ],
+    ["Date.UTC(2020, 0, 2)", 1577923200000],
+  ])("preserves %s", async (expression, expected) => {
+    const workerRequest = await request("parser.mjs", "esm", "default", []);
+    workerRequest.left.modules[0] = {
+      alias: "entry",
+      format: "esm",
+      dependencies: {},
+      source: `export default function () { return ${expression}; }`,
+    };
+    const result = await runWorker(workerRequest);
+    expect(result.code).toBe(0);
+    expect(JSON.parse(result.stdout)).toMatchObject({
+      left: [{ outcome: "return", value: expected }],
+    });
+  });
+});
+
 describe("replay array projection", () => {
   it.each([
     ["Array(3)", [null, null, null]],