Execution Timing

October 1, 2020

Measuring the time of JavaScript execution in a browser can give attackers information on when certain events are triggered, and how long some operations take.

Timing the Event Loop #

JavaScript’s concurrency model is based on a single-threaded event loop which means it can only run one task at a time. If, for example, some time-consuming task blocks the event loop, the user can perceive a freeze on a page as a result of the UI thread being starved. Other tasks must wait until the blocking task finishes. Each browser implements different process models, which means some web sites might run in different threads (and event loops) depending on their relations.