JavaScript Runtime Environment in the Browser According to the HTML Standard: Agents, Event Loop, Tasks, and Microtasks

This article on Habr provides an in-depth analysis of how the JavaScript runtime environment actually works in browsers according to the HTML specification. The author notes that the simplified views of the event loop often encountered in interviews do not always reflect reality. Notably, the term 'macrotask' does not exist in the standard; instead, they are simply referred to as 'tasks'. The article covers aspects such as agent interaction, the impact of window.open on thread behavior, and the nuances of microtask execution. The author emphasizes that understanding the standard is essential for predicting code behavior in complex scenarios where tabs may affect each other or execution order depends on the calling context. This material is useful for developers looking to go beyond superficial knowledge of browser engine mechanics and understand the architectural intricacies of the web platform.