Performance guides

This first batch publishes 3 of the 30 upstream Performance guides; the rest are converted and will be released in later batches.

• Break Up Long Tasks — Break up heavy synchronous processing (complex computations and/or long loops) or DOM updates to improve Interaction to Next Paint (INP) responsiveness and let the browser handle user input and repaint the screen.
• Identify causes of poor INP — Identify slow-running JavaScript and other causes of poor Interaction to Next Paint (INP) responsiveness.
• Lazy load video and audio — Defer downloading offscreen video and audio assets, including video poster images and preloaded media data, until the media player approaches the viewport to conserve bandwidth and reduce network contention during initial page load.