From d01054b73b42980c13137720a3f43152f086de0a Mon Sep 17 00:00:00 2001
From: David Luna <david.luna@elastic.co>
Date: Wed, 23 Jul 2025 11:55:58 +0200
Subject: [PATCH 1/3] feat: add esm output

---
 packages/instrumentation-undici/package.json  | 26 ++++++++++++++++---
 packages/instrumentation-undici/src/index.ts  |  4 +--
 .../src/internal-types.ts                     |  2 +-
 packages/instrumentation-undici/src/undici.ts |  8 +++---
 .../instrumentation-undici/test/fetch.test.ts |  8 +++---
 .../test/metrics.test.ts                      |  8 +++---
 .../test/undici.test.ts                       |  8 +++---
 .../test/utils/assertSpan.ts                  |  2 +-
 .../instrumentation-undici/tsconfig.esm.json  | 11 ++++++++
 packages/instrumentation-undici/tsconfig.json |  4 ++-
 10 files changed, 57 insertions(+), 24 deletions(-)
 create mode 100644 packages/instrumentation-undici/tsconfig.esm.json

diff --git a/packages/instrumentation-undici/package.json b/packages/instrumentation-undici/package.json
index 2069b893f1..790a86af4c 100644
--- a/packages/instrumentation-undici/package.json
+++ b/packages/instrumentation-undici/package.json
@@ -3,7 +3,9 @@
   "version": "0.14.0",
   "description": "OpenTelemetry instrumentation for `undici` http client and Node.js fetch()",
   "main": "build/src/index.js",
+  "module": "build/esm/index.js",
   "types": "build/src/index.d.ts",
+  "type": "module",
   "repository": {
     "type": "git",
     "url": "https://github.com/open-telemetry/opentelemetry-js-contrib.git",
@@ -12,11 +14,13 @@
   "scripts": {
     "prepublishOnly": "npm run compile",
     "setup:dev": "nx run-many -t compile -p @opentelemetry/instrumentation-undici",
-    "compile": "tsc -p .",
+    "compile": "npm run compile:cjs && npm run compile:esm",
+    "compile:cjs": "tsc --build tsconfig.json && echo '{ \"type\": \"commonjs\" }' > build/src/package.json",
+    "compile:esm": "tsc --build tsconfig.esm.json",
+    "clean": "tsc --build --clean tsconfig.json tsconfig.esm.json",
     "test": "nyc mocha test/**/*.test.ts",
     "test-all-versions": "tav",
     "tdd": "npm run test -- --watch-extensions ts --watch",
-    "clean": "rimraf build/*",
     "lint": "eslint . --ext .ts",
     "lint:fix": "eslint . --ext .ts --fix",
     "watch": "tsc -w",
@@ -35,10 +39,26 @@
   "engines": {
     "node": "^18.19.0 || >=20.6.0"
   },
+  "exports": {
+    "import": {
+      "types": "./build/esm/index.d.ts",
+      "default": "./build/esm/index.js"
+    },
+    "require": {
+      "types": "./build/src/index.d.ts",
+      "default": "./build/src/index.js"
+    }
+  },
   "files": [
     "build/src/**/*.js",
     "build/src/**/*.js.map",
-    "build/src/**/*.d.ts"
+    "build/src/**/*.d.ts",
+    "build/src/**/*.js",
+    "build/src/**/*.js.map",
+    "build/src/**/*.d.ts",
+    "build/esm/**/*.js",
+    "build/esm/**/*.js.map",
+    "build/esm/**/*.d.ts"
   ],
   "publishConfig": {
     "access": "public"
diff --git a/packages/instrumentation-undici/src/index.ts b/packages/instrumentation-undici/src/index.ts
index 942dd61bb7..c0de41cfdd 100644
--- a/packages/instrumentation-undici/src/index.ts
+++ b/packages/instrumentation-undici/src/index.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-export { UndiciInstrumentation } from './undici';
+export { UndiciInstrumentation } from './undici.js';
 export type {
   IgnoreRequestFunction,
   RequestHookFunction,
@@ -23,4 +23,4 @@ export type {
   UndiciInstrumentationConfig,
   UndiciRequest,
   UndiciResponse,
-} from './types';
+} from './types.js';
diff --git a/packages/instrumentation-undici/src/internal-types.ts b/packages/instrumentation-undici/src/internal-types.ts
index e6b2fff535..3e7c2645a0 100644
--- a/packages/instrumentation-undici/src/internal-types.ts
+++ b/packages/instrumentation-undici/src/internal-types.ts
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-import { UndiciRequest, UndiciResponse } from './types';
+import { UndiciRequest, UndiciResponse } from './types.js';
 
 export interface ListenerRecord {
   name: string;
diff --git a/packages/instrumentation-undici/src/undici.ts b/packages/instrumentation-undici/src/undici.ts
index 519ba4691f..666f1bce6f 100644
--- a/packages/instrumentation-undici/src/undici.ts
+++ b/packages/instrumentation-undici/src/undici.ts
@@ -35,7 +35,7 @@ import {
 } from '@opentelemetry/api';
 
 /** @knipignore */
-import { PACKAGE_NAME, PACKAGE_VERSION } from './version';
+import { PACKAGE_NAME, PACKAGE_VERSION } from './version.js';
 
 import {
   ListenerRecord,
@@ -43,9 +43,9 @@ import {
   RequestMessage,
   RequestTrailersMessage,
   ResponseHeadersMessage,
-} from './internal-types';
-import { UndiciInstrumentationConfig, UndiciRequest } from './types';
-import { SemanticAttributes } from './enums/SemanticAttributes';
+} from './internal-types.js';
+import { UndiciInstrumentationConfig, UndiciRequest } from './types.js';
+import { SemanticAttributes } from './enums/SemanticAttributes.js';
 import {
   hrTime,
   hrTimeDuration,
diff --git a/packages/instrumentation-undici/test/fetch.test.ts b/packages/instrumentation-undici/test/fetch.test.ts
index 7e389838bb..becc772f5d 100644
--- a/packages/instrumentation-undici/test/fetch.test.ts
+++ b/packages/instrumentation-undici/test/fetch.test.ts
@@ -29,11 +29,11 @@ import {
 } from '@opentelemetry/sdk-trace-base';
 import { NodeTracerProvider } from '@opentelemetry/sdk-trace-node';
 
-import { UndiciInstrumentation } from '../src/undici';
+import { UndiciInstrumentation } from '../src/undici.js';
 
-import { MockPropagation } from './utils/mock-propagation';
-import { MockServer } from './utils/mock-server';
-import { assertSpan } from './utils/assertSpan';
+import { MockPropagation } from './utils/mock-propagation.js';
+import { MockServer } from './utils/mock-server.js';
+import { assertSpan } from './utils/assertSpan.js';
 
 describe('UndiciInstrumentation `fetch` tests', function () {
   let instrumentation: UndiciInstrumentation;
diff --git a/packages/instrumentation-undici/test/metrics.test.ts b/packages/instrumentation-undici/test/metrics.test.ts
index bca94ac6e9..ecad70cdcb 100644
--- a/packages/instrumentation-undici/test/metrics.test.ts
+++ b/packages/instrumentation-undici/test/metrics.test.ts
@@ -25,11 +25,11 @@ import {
   MeterProvider,
 } from '@opentelemetry/sdk-metrics';
 
-import { UndiciInstrumentation } from '../src/undici';
+import { UndiciInstrumentation } from '../src/undici.js';
 
-import { MockServer } from './utils/mock-server';
-import { MockMetricsReader } from './utils/mock-metrics-reader';
-import { SemanticAttributes } from '../src/enums/SemanticAttributes';
+import { MockServer } from './utils/mock-server.js';
+import { MockMetricsReader } from './utils/mock-metrics-reader.js';
+import { SemanticAttributes } from '../src/enums/SemanticAttributes.js';
 
 describe('UndiciInstrumentation metrics tests', function () {
   let instrumentation: UndiciInstrumentation;
diff --git a/packages/instrumentation-undici/test/undici.test.ts b/packages/instrumentation-undici/test/undici.test.ts
index 2a124fb199..991eb29b04 100644
--- a/packages/instrumentation-undici/test/undici.test.ts
+++ b/packages/instrumentation-undici/test/undici.test.ts
@@ -31,11 +31,11 @@ import {
 } from '@opentelemetry/sdk-trace-base';
 import { NodeTracerProvider } from '@opentelemetry/sdk-trace-node';
 
-import { UndiciInstrumentation } from '../src/undici';
+import { UndiciInstrumentation } from '../src/undici.js';
 
-import { MockPropagation } from './utils/mock-propagation';
-import { MockServer } from './utils/mock-server';
-import { assertSpan } from './utils/assertSpan';
+import { MockPropagation } from './utils/mock-propagation.js';
+import { MockServer } from './utils/mock-server.js';
+import { assertSpan } from './utils/assertSpan.js';
 
 import type { fetch, stream, request, Client, Dispatcher } from 'undici';
 
diff --git a/packages/instrumentation-undici/test/utils/assertSpan.ts b/packages/instrumentation-undici/test/utils/assertSpan.ts
index c5d584dd46..271ace0a9a 100644
--- a/packages/instrumentation-undici/test/utils/assertSpan.ts
+++ b/packages/instrumentation-undici/test/utils/assertSpan.ts
@@ -22,7 +22,7 @@ import {
 import { hrTimeToNanoseconds } from '@opentelemetry/core';
 import { ReadableSpan } from '@opentelemetry/sdk-trace-base';
 import * as assert from 'assert';
-import { SemanticAttributes } from '../../src/enums/SemanticAttributes';
+import { SemanticAttributes } from '../../src/enums/SemanticAttributes.js';
 
 type IncomingHttpHeaders = Record<string, string | string[] | undefined>;
 
diff --git a/packages/instrumentation-undici/tsconfig.esm.json b/packages/instrumentation-undici/tsconfig.esm.json
new file mode 100644
index 0000000000..f97a35348f
--- /dev/null
+++ b/packages/instrumentation-undici/tsconfig.esm.json
@@ -0,0 +1,11 @@
+{
+  "extends": "../../tsconfig.base.esm.json",
+  "compilerOptions": {
+    "outDir": "build/esm",
+    "rootDir": "src",
+    "tsBuildInfoFile": "build/esm/tsconfig.esm.tsbuildinfo"
+  },
+  "include": [
+    "src/**/*.ts"
+  ]
+}
diff --git a/packages/instrumentation-undici/tsconfig.json b/packages/instrumentation-undici/tsconfig.json
index 4078877ce6..c3975a475d 100644
--- a/packages/instrumentation-undici/tsconfig.json
+++ b/packages/instrumentation-undici/tsconfig.json
@@ -2,7 +2,9 @@
   "extends": "../../tsconfig.base",
   "compilerOptions": {
     "rootDir": ".",
-    "outDir": "build"
+    "outDir": "build",
+    "module": "commonjs",
+    "moduleResolution": "node10"
   },
   "include": [
     "src/**/*.ts",

From 8058096c4398f40e3db42705f067f9c1a8d3ad8e Mon Sep 17 00:00:00 2001
From: David Luna <david.luna@elastic.co>
Date: Wed, 23 Jul 2025 17:27:48 +0200
Subject: [PATCH 2/3] chore: fix lint script

---
 packages/instrumentation-undici/{.eslintrc.js => .eslintrc.cjs} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename packages/instrumentation-undici/{.eslintrc.js => .eslintrc.cjs} (100%)

diff --git a/packages/instrumentation-undici/.eslintrc.js b/packages/instrumentation-undici/.eslintrc.cjs
similarity index 100%
rename from packages/instrumentation-undici/.eslintrc.js
rename to packages/instrumentation-undici/.eslintrc.cjs

From 0ea999597900616727c05369c1ac318c6e3d48f2 Mon Sep 17 00:00:00 2001
From: David Luna <david.luna@elastic.co>
Date: Thu, 24 Jul 2025 16:03:18 +0200
Subject: [PATCH 3/3] chore: change compilation targets

---
 packages/instrumentation-undici/package.json  | 25 ++++++++-----------
 .../test/undici.test.ts                       |  7 ++++++
 .../instrumentation-undici/tsconfig.cjs.json  | 13 ++++++++++
 .../instrumentation-undici/tsconfig.esm.json  | 11 --------
 packages/instrumentation-undici/tsconfig.json |  8 +++---
 5 files changed, 34 insertions(+), 30 deletions(-)
 create mode 100644 packages/instrumentation-undici/tsconfig.cjs.json
 delete mode 100644 packages/instrumentation-undici/tsconfig.esm.json

diff --git a/packages/instrumentation-undici/package.json b/packages/instrumentation-undici/package.json
index 790a86af4c..fbc952a906 100644
--- a/packages/instrumentation-undici/package.json
+++ b/packages/instrumentation-undici/package.json
@@ -14,11 +14,9 @@
   "scripts": {
     "prepublishOnly": "npm run compile",
     "setup:dev": "nx run-many -t compile -p @opentelemetry/instrumentation-undici",
-    "compile": "npm run compile:cjs && npm run compile:esm",
-    "compile:cjs": "tsc --build tsconfig.json && echo '{ \"type\": \"commonjs\" }' > build/src/package.json",
-    "compile:esm": "tsc --build tsconfig.esm.json",
-    "clean": "tsc --build --clean tsconfig.json tsconfig.esm.json",
-    "test": "nyc mocha test/**/*.test.ts",
+    "compile": "tsc --build tsconfig.json tsconfig.cjs.json && echo '{\"type\":\"commonjs\"}' > build/cjs/package.json",
+    "clean": "tsc --build --clean tsconfig.json tsconfig.cjs.json",
+    "test": "nyc mocha --loader=ts-node/esm test/**/*.test.ts",
     "test-all-versions": "tav",
     "tdd": "npm run test -- --watch-extensions ts --watch",
     "lint": "eslint . --ext .ts",
@@ -41,24 +39,21 @@
   },
   "exports": {
     "import": {
-      "types": "./build/esm/index.d.ts",
-      "default": "./build/esm/index.js"
-    },
-    "require": {
       "types": "./build/src/index.d.ts",
       "default": "./build/src/index.js"
+    },
+    "require": {
+      "types": "./build/cjs/index.d.ts",
+      "default": "./build/cjs/index.js"
     }
   },
   "files": [
     "build/src/**/*.js",
     "build/src/**/*.js.map",
     "build/src/**/*.d.ts",
-    "build/src/**/*.js",
-    "build/src/**/*.js.map",
-    "build/src/**/*.d.ts",
-    "build/esm/**/*.js",
-    "build/esm/**/*.js.map",
-    "build/esm/**/*.d.ts"
+    "build/cjs/**/*.js",
+    "build/cjs/**/*.js.map",
+    "build/cjs/**/*.d.ts"
   ],
   "publishConfig": {
     "access": "public"
diff --git a/packages/instrumentation-undici/test/undici.test.ts b/packages/instrumentation-undici/test/undici.test.ts
index 991eb29b04..c44ea33f37 100644
--- a/packages/instrumentation-undici/test/undici.test.ts
+++ b/packages/instrumentation-undici/test/undici.test.ts
@@ -15,6 +15,7 @@
  */
 import * as assert from 'assert';
 import { Writable } from 'stream';
+import { createRequire } from 'module';
 
 import {
   INVALID_SPAN_CONTEXT,
@@ -39,6 +40,12 @@ import { assertSpan } from './utils/assertSpan.js';
 
 import type { fetch, stream, request, Client, Dispatcher } from 'undici';
 
+// NOTE: now this test is compiled to ESM and `require` is not available.
+// So we do this to not make a refactor on code that is not publishwd to the user.
+// This could be handled once https://github.com/open-telemetry/opentelemetry-js/issues/4898
+// is closed.
+const require = createRequire(import.meta.url);
+
 // Undici docs (https://github.com/nodejs/undici#garbage-collection) suggest
 // that an undici response body should always be consumed.
 async function consumeResponseBody(body: Dispatcher.ResponseData['body']) {
diff --git a/packages/instrumentation-undici/tsconfig.cjs.json b/packages/instrumentation-undici/tsconfig.cjs.json
new file mode 100644
index 0000000000..9b87ebb819
--- /dev/null
+++ b/packages/instrumentation-undici/tsconfig.cjs.json
@@ -0,0 +1,13 @@
+{
+  "extends": "../../tsconfig.base",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "build/cjs",
+    "module": "commonjs",
+    "moduleResolution": "node10",
+    "tsBuildInfoFile": "build/cjs/tsconfig.cjs.tsbuildinfo"
+  },
+  "include": [
+    "src/**/*.ts"
+  ]
+}
diff --git a/packages/instrumentation-undici/tsconfig.esm.json b/packages/instrumentation-undici/tsconfig.esm.json
deleted file mode 100644
index f97a35348f..0000000000
--- a/packages/instrumentation-undici/tsconfig.esm.json
+++ /dev/null
@@ -1,11 +0,0 @@
-{
-  "extends": "../../tsconfig.base.esm.json",
-  "compilerOptions": {
-    "outDir": "build/esm",
-    "rootDir": "src",
-    "tsBuildInfoFile": "build/esm/tsconfig.esm.tsbuildinfo"
-  },
-  "include": [
-    "src/**/*.ts"
-  ]
-}
diff --git a/packages/instrumentation-undici/tsconfig.json b/packages/instrumentation-undici/tsconfig.json
index c3975a475d..4d1e4c9930 100644
--- a/packages/instrumentation-undici/tsconfig.json
+++ b/packages/instrumentation-undici/tsconfig.json
@@ -1,10 +1,10 @@
 {
-  "extends": "../../tsconfig.base",
+  "extends": "../../tsconfig.base.esm.json",
   "compilerOptions": {
-    "rootDir": ".",
     "outDir": "build",
-    "module": "commonjs",
-    "moduleResolution": "node10"
+    "rootDir": ".",
+    "module": "node16",
+    "tsBuildInfoFile": "build/src/tsconfig.esm.tsbuildinfo"
   },
   "include": [
     "src/**/*.ts",