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Next.js 16+ · Directive

instrumentation-client

Use instrumentation-client.js or .ts for client monitoring, analytics, error tracking, and other side effects before the app becomes interactive. Put it at the app root or in src; export onRouterTransitionStart to observe App Router navigation starts.

Last updated

Since
v15.3

Syntax

instrumentation-client.js|ts
export function onRouterTransitionStart(url: string, navigationType: 'push' | 'replace' | 'traverse') { }

In-depth API docs are only for subscribers: parameters, examples, common mistakes and interview practice.

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  • onRouterTransitionStart
  • instrumentationClientRouterTransitionEvents
  • RouterTransitionStartEvent
  • RouterTransitionType
  • useReportWebVitals
  • Custom Polyfills

Source: instrumentation-client.js. Checked 2026-11-03.