This is the sixth article in a series on how JavaScript actually runs. You can read the full series here or on my website . In the last article , we established that: The browser will not render while a macrotask is running nor while microtasks are draining. Instead, rendering only happens at stable boundaries. But this creates a new problem: If rendering only happens at specific boundaries, how do we run code just before a render? If we want smooth animation, frame-aligned updates, or visual state that reflects the latest input, we need something that runs once per frame right before the browser renders. That is the scheduling gap that requestAnimationFrame fills. Running the Experiments These experiments rely on the browser’s rendering behaviour. Create a simple HTML file with the following content: <div id= "box" > Initial </div> Enter fullscreen mode Exit fullscreen mode Open the file in your browser You can run all code snippets in this series by pasting them into the browser console.…