log the instrumentation-client execution time (#77121)

Follow up to
#76916 (comment)


![CleanShot 2025-03-14 at
[email protected]](https://graphite-user-uploaded-assets-prod.s3.amazonaws.com/rKSEEwxbNzdFs9t0yyxN/13cbdcea-02c2-41b4-9219-103b1dbf545e.png)

Author: gaojude

packages/next/src/lib/require-instrumentation-client.ts

@@ -4,7 +4,15 @@
  * The `private-next-instrumentation-client` module is automatically aliased to
  * the `instrumentation-client.ts` file in the project root by webpack or turbopack.
  */
-
 if (process.env.__NEXT_EXPERIMENTAL_CLIENT_INSTRUMENTATION_HOOK) {
-  require('private-next-instrumentation-client')
+  if (process.env.NODE_ENV === 'development') {
+    const startTime = performance.now()
+    require('private-next-instrumentation-client')
+    const endTime = performance.now()
+    console.log(
+      `[Client Instrumentation Hook] executed in ${(endTime - startTime).toFixed(0)}ms (Note: Code download overhead is not included in this measurement)`
+    )
+  } else {
+    require('private-next-instrumentation-client')
+  }
 }

test/e2e/instrumentation-client-hook/instrumentation-client-hook.test.ts

@@ -20,7 +20,7 @@ describe('Instrumentation Client Hook', () => {
 
   testCases.forEach(({ name, appDir }) => {
     describe(name, () => {
-      const { next } = nextTestSetup({
+      const { next, isNextDev } = nextTestSetup({
         files: path.join(__dirname, appDir),
       })
 
@@ -35,6 +35,11 @@ describe('Instrumentation Client Hook', () => {
         expect(instrumentationTime).toBeDefined()
         expect(hydrationTime).toBeDefined()
         expect(instrumentationTime).toBeLessThan(hydrationTime)
+        expect(
+          (await browser.log()).some((log) =>
+            log.message.startsWith('[Client Instrumentation Hook]')
+          )
+        ).toBe(isNextDev)
       })
     })
   })