Discuss react profiler.

0-2 years experience

1. 1We have a product list page that feels sluggish when typing in a search filter. How would you use the React DevTools Profiler to find out which specific component in the list is taking the longest to render?
2. 2Imagine you've wrapped a component in React's `<Profiler>` component. In the `onRender` callback, you see a high 'actual duration' but a low 'base duration'. What does this tell you about that component's render phase versus its children?

2-5 years experience

1. 1A team member claims that wrapping our entire app in the `<Profiler>` component is causing a noticeable lag in our staging environment. How would you explain the overhead of the Profiler to them, and how would you selectively profile only the problematic dashboard widgets instead?
2. 2You are profiling a form component and notice in the DevTools Profiler that a heavy chart component is re-rendering on every single keystroke. The chart's props haven't changed. How would you use the Profiler's commit data to prove why it's re-rendering, and what steps would you take to fix it?

5-8 years experience

1. 1We want to set up automated performance monitoring in our production environment to catch slow renders on our checkout page. How would you configure React's programmatic `<Profiler>` API to send render metrics to our analytics endpoint without degrading the user experience?
2. 2During a performance audit of a complex dashboard, the Profiler shows a long 'commit phase' but very short 'render phases' for individual components. What kinds of operations usually cause a bottleneck in the commit phase rather than the render phase, and how would you resolve this?

8+ years experience

1. 1Our enterprise SaaS application has over 200 micro-frontends managed by different teams, and we're seeing systemic interaction delays (INP). How would you design a standardized, low-overhead profiling and telemetry strategy using React's Profiler API to enforce performance budgets across these distributed teams?
2. 2We are planning a migration from React 17 to React 18 with Concurrent Features enabled. How does the introduction of transitions, deferred values, and suspended state changes alter how we interpret Profiler data, and how would you train the engineering org to debug performance in this new concurrent paradigm?