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Chapter 10

  • The execution of a web app involves three tasks
    1. Fetch resources
    2. page layout and rendering
    3. Javascript execution

The rendering and scripting steps are symmetric, it is not possible to run them concurrently.

The Navigation Timing API is included in most modern web browsers. It can be used for a wholistic view of page load timing. It includes DNS and TCP connect times with high precision. The Resource Timing API is also included with most modern browsers can can be used to view the performance profile of a page. The User Timing API provides a simple JavaScript API to mark and measure application-specific performance metrics with the help of high-resolution timers.