From cd5e4f9f9dfec525912802392696b4a78df4ec59 Mon Sep 17 00:00:00 2001
From: Sean LeCheminant <taxable.honeyed_06@icloud.com>
Date: Thu, 5 Feb 2026 15:27:28 -0600
Subject: [PATCH 1/3] fix: Extracting waitUntil and calling it directly is
 losing its this context.

---
 packages/evlog/src/nitro/plugin.ts | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/packages/evlog/src/nitro/plugin.ts b/packages/evlog/src/nitro/plugin.ts
index 18d61a2..f9cfc3a 100644
--- a/packages/evlog/src/nitro/plugin.ts
+++ b/packages/evlog/src/nitro/plugin.ts
@@ -119,11 +119,12 @@ function callDrainHook(nitroApp: NitroApp, emittedEvent: WideEvent | null, event
 
   // Use waitUntil if available (Cloudflare Workers, Vercel Edge)
   // This ensures drains complete before the runtime terminates
-  const waitUntil = event.context.cloudflare?.context?.waitUntil
-    ?? event.context.waitUntil
+  const cfContext = event.context.cloudflare?.context
 
-  if (typeof waitUntil === 'function') {
-    waitUntil(drainPromise)
+  if (cfContext && typeof cfContext.waitUntil === 'function') {
+    cfContext.waitUntil(drainPromise)
+  } else if (event.context.waitUntil && typeof event.context.waitUntil === 'function') {
+    event.context.waitUntil(drainPromise)
   }
 }
 

From 3f3f88705233e0cd394d1e8f561914c29fa5bc44 Mon Sep 17 00:00:00 2001
From: Sean LeCheminant <taxable.honeyed_06@icloud.com>
Date: Thu, 5 Feb 2026 15:39:06 -0600
Subject: [PATCH 2/3] simplified

---
 packages/evlog/src/nitro/plugin.ts | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/packages/evlog/src/nitro/plugin.ts b/packages/evlog/src/nitro/plugin.ts
index f9cfc3a..75728d3 100644
--- a/packages/evlog/src/nitro/plugin.ts
+++ b/packages/evlog/src/nitro/plugin.ts
@@ -119,12 +119,9 @@ function callDrainHook(nitroApp: NitroApp, emittedEvent: WideEvent | null, event
 
   // Use waitUntil if available (Cloudflare Workers, Vercel Edge)
   // This ensures drains complete before the runtime terminates
-  const cfContext = event.context.cloudflare?.context
-
-  if (cfContext && typeof cfContext.waitUntil === 'function') {
-    cfContext.waitUntil(drainPromise)
-  } else if (event.context.waitUntil && typeof event.context.waitUntil === 'function') {
-    event.context.waitUntil(drainPromise)
+  const waitUntilCtx = event.context.cloudflare?.context ?? event.context
+  if (typeof waitUntilCtx?.waitUntil === 'function') {
+    waitUntilCtx.waitUntil(drainPromise)
   }
 }
 

From 07edc7669b94f07a8158515cfd2317e3f80f206e Mon Sep 17 00:00:00 2001
From: Hugo Richard <hugo.richard@vercel.com>
Date: Sat, 7 Feb 2026 17:51:30 +0000
Subject: [PATCH 3/3] fix tests

---
 packages/evlog/test/nitro-plugin.test.ts | 52 +++++++++++++++++++++---
 1 file changed, 47 insertions(+), 5 deletions(-)

diff --git a/packages/evlog/test/nitro-plugin.test.ts b/packages/evlog/test/nitro-plugin.test.ts
index 92854de..5a3332f 100644
--- a/packages/evlog/test/nitro-plugin.test.ts
+++ b/packages/evlog/test/nitro-plugin.test.ts
@@ -317,11 +317,10 @@ describe('nitro plugin - waitUntil support', () => {
     })
 
     // Use waitUntil if available (Cloudflare Workers, Vercel Edge)
-    const waitUntil = event.context.cloudflare?.context?.waitUntil
-      ?? event.context.waitUntil
-
-    if (typeof waitUntil === 'function') {
-      waitUntil(drainPromise)
+    // Call as a method on the context object to preserve `this` binding
+    const waitUntilCtx = event.context.cloudflare?.context ?? event.context
+    if (typeof waitUntilCtx?.waitUntil === 'function') {
+      waitUntilCtx.waitUntil(drainPromise)
     }
   }
 
@@ -448,6 +447,49 @@ describe('nitro plugin - waitUntil support', () => {
     expect(mockHooks.callHook).toHaveBeenCalledWith('evlog:drain', expect.any(Object))
   })
 
+  it('preserves this binding when calling waitUntil (prevents Illegal invocation)', () => {
+    // Simulate a real waitUntil that requires correct `this` binding,
+    // like Cloudflare's ExecutionContext which throws "Illegal invocation"
+    // when `waitUntil` is called without proper `this` context
+    const executionContext = {
+      _promises: [] as Promise<unknown>[],
+      waitUntil(promise: Promise<unknown>) {
+        if (this !== executionContext) {
+          throw new TypeError('Illegal invocation')
+        }
+        this._promises.push(promise)
+      },
+    }
+
+    const mockHooks = {
+      callHook: vi.fn().mockResolvedValue(undefined),
+    }
+
+    const mockEvent: ServerEvent = {
+      method: 'POST',
+      path: '/api/test',
+      context: {
+        cloudflare: {
+          context: executionContext,
+        },
+      },
+    }
+
+    const mockEmittedEvent: WideEvent = {
+      timestamp: new Date().toISOString(),
+      level: 'info',
+      service: 'test',
+      environment: 'production',
+    }
+
+    // Should NOT throw "Illegal invocation" because waitUntil is called as a method
+    expect(() => {
+      callDrainHook({ hooks: mockHooks }, mockEmittedEvent, mockEvent)
+    }).not.toThrow()
+
+    expect(executionContext._promises).toHaveLength(1)
+  })
+
   it('does not call waitUntil when emittedEvent is null', () => {
     const mockWaitUntil = vi.fn()
     const mockHooks = {