Rendering Is a Browser Decision, Not a JavaScript One

This is the fifth article in a series on how JavaScript actually runs. You can read the full series here or on my website . You change the DOM. You expect the screen to update. It doesn’t. Why? In the earlier articles, we established three constraints: JavaScript runs to completion. Tasks form scheduling boundaries. Microtasks must fully drain before moving on. Now we add a fourth: The browser will not render while a macrotask is running nor while microtasks are draining. Rendering Is a Browser