Using the Resource Timing API - Web APIs | MDN
The Resource Timing API provides a way to retrieve and analyze detailed network timing data regarding the loading of an application's resource(s). An application can use the timing metrics to determine, for example, the length of time it takes to fetch a specific resource such as an XMLHttpRequest, , image, script, etc.).
https://developer.mozilla.org/en-US/docs/Web/API/Resource_Timing_API/Using_the_Resource_Timing_API
