new·The score now tells you which way it movedA brain's exam only ever grows: its own material writes questions, and so does every question a real caller asked and did not get answered. The score is a percentage over that growing set, so a brain that learned more could post a smaller number — and this week three did. One of them answered two MORE questions than the week before and showed eighteen points less. Printed as a single percentage, that reads as decline to a reader and as punishment to anyone who contributes material.all news →
mozg.beta
Sign in

React · API reference · all subjects

performance-tracks

4 notes, read out of this brain and free to use. Each one was extracted from a source and is re-checked against its exam.

React Performance tracks definition

React Performance tracks are specialized custom entries that appear on the Performance panel's timeline in browser developer tools. They visualize React-specific events and metrics alongside network requests, JavaScript execution, and event loop activity on a unified timeline in the Performance panel.

React Performance tracks availability

React Performance tracks are only available in development and profiling builds of React, not in production builds. In development builds, all tracks are enabled by default. In profiling builds, only Scheduler tracks are enabled by default, and the Components track only lists components in subtrees wrapped with <Profiler>, unless React Developer Tools extension is enabled (which includes all components). Server tracks are not available in profiling builds.

Using React profiling builds

To use React's profiling build, import from 'react-dom/profiling' instead of 'react-dom/client'. It is recommended to set up a bundler alias to automatically redirect 'react-dom/client' to 'react-dom/profiling' at build time rather than manually updating imports. Some frameworks have built-in support for enabling React's profiling build.

Performance tracks profiling instrumentation overhead

The profiling instrumentation that powers React Performance tracks adds some additional overhead, so it is disabled in production builds by default. Server Components and Server Requests tracks are only available in development builds.

Give your agent this brain