From 5981dde6d77dbfe443f1ece963a37c3035b4690d Mon Sep 17 00:00:00 2001
From: Benoit Zugmeyer <benoit.zugmeyer@datadoghq.com>
Date: Fri, 19 Dec 2025 15:21:50 +0100
Subject: [PATCH] fix(instrumentation-web-exception): properly add bounded
 error listener

The README.md advises to use the instrumentation like this:

```
registerInstrumentations({
  instrumentations: [
    new ExceptionInstrumentation({ ... }),
  ],
});
```

But this does not work because the function passed to
`addEventListener('error', ...)` is the unbounded method, so accesses to
`this.getConfig()` failed.

I know this sounds surprising, because the `onError` method was properly
reaffected with the bounded method in the constructor. But actually,
`enable()` is called by the base class, during `super()`, which is
called *before the `onError` is bound*!

This wasn't caught in tests because in test, `enable()` is called two
times, once when instantiating the instrumentation, and once explicitely
when calling `instr.enable()`. This second call *do* register the
correctly bounded method.

To work around this, this PR make sure the `onError` method is proprely
bound in `enable()`.
---
 .../src/instrumentation.ts                    |  2 +-
 .../test/instrumentation.test.ts              | 29 ++++++++++---------
 2 files changed, 16 insertions(+), 15 deletions(-)

diff --git a/packages/instrumentation-web-exception/src/instrumentation.ts b/packages/instrumentation-web-exception/src/instrumentation.ts
index 2972740906..0a5da75b46 100644
--- a/packages/instrumentation-web-exception/src/instrumentation.ts
+++ b/packages/instrumentation-web-exception/src/instrumentation.ts
@@ -49,7 +49,6 @@ export interface GlobalErrorsInstrumentationConfig
 export class ExceptionInstrumentation extends InstrumentationBase<GlobalErrorsInstrumentationConfig> {
   constructor(config: GlobalErrorsInstrumentationConfig = {}) {
     super(PACKAGE_NAME, PACKAGE_VERSION, config);
-    this.onError = this.onError.bind(this);
   }
 
   init() {}
@@ -101,6 +100,7 @@ export class ExceptionInstrumentation extends InstrumentationBase<GlobalErrorsIn
   }
 
   override enable(): void {
+    this.onError = this.onError.bind(this);
     window.addEventListener('error', this.onError);
     window.addEventListener('unhandledrejection', this.onError);
   }
diff --git a/packages/instrumentation-web-exception/test/instrumentation.test.ts b/packages/instrumentation-web-exception/test/instrumentation.test.ts
index aba34a528c..05b98016c4 100644
--- a/packages/instrumentation-web-exception/test/instrumentation.test.ts
+++ b/packages/instrumentation-web-exception/test/instrumentation.test.ts
@@ -98,17 +98,15 @@ describe('ExceptionInstrumentation', () => {
   });
 
   describe('throwing an error', () => {
-    const instr = new ExceptionInstrumentation();
+    let disableInstrumentations: () => void;
     beforeEach(() => {
-      registerInstrumentations({
-        instrumentations: [instr],
+      disableInstrumentations = registerInstrumentations({
+        instrumentations: [new ExceptionInstrumentation()],
       });
-
-      instr.enable();
     });
 
     afterEach(() => {
-      instr.disable();
+      disableInstrumentations();
       exporter.reset();
     });
 
@@ -179,21 +177,24 @@ describe('ExceptionInstrumentation', () => {
         'app.custom.exception': error.message.toLocaleUpperCase(),
       };
     };
-    const instr = new ExceptionInstrumentation({
-      applyCustomAttributes: applyCustomAttrs,
-    });
+
+    let disableInstrumentations: () => void;
+
     beforeEach(() => {
-      registerInstrumentations({
-        instrumentations: [instr],
+      disableInstrumentations = registerInstrumentations({
+        instrumentations: [
+          new ExceptionInstrumentation({
+            applyCustomAttributes: applyCustomAttrs,
+          }),
+        ],
       });
-
-      instr.enable();
     });
 
     afterEach(() => {
-      instr.disable();
+      disableInstrumentations();
       exporter.reset();
     });
+
     it('should add custom attributes to the event', async () => {
       setTimeout(() => {
         throwErr('Something happened!');