What is DOM Reflow and How Does it Impact Webpage Rendering?

Understanding DOM Reflow

While exploring the distinction between CSS properties display: none and visibility: hidden, the term "DOM reflow" surfaced. This article delves into the concept of DOM reflow and its mechanics.

What is DOM Reflow?

DOM reflow is the process of calculating the layout of a webpage. It involves determining the dimensions and positions of elements within the Document Object Model (DOM). When a reflow event is triggered on an element, it necessitates subsequent reflows on its children, ancestors, and elements that follow it in the DOM hierarchy. This resource-intensive process culminates in a repainting of the page.

Triggers of DOM Reflow

Reflows are commonly initiated by the following actions:

• Inserting, removing, or modifying elements within the DOM
• Modifying content on the page (e.g., text input)
• Moving or animating DOM elements
• Taking measurements of DOM elements
• Altering CSS styles or class names
• Adding or removing stylesheets
• Resizing the browser window
• Scrolling

Understanding Repaints

Reflows and repaints are distinct processes in the rendering pipeline. Reflows determine the layout of elements, while repaints involve updating the actual display on the screen. While repaints can be triggered by reflows, they can also occur independently (e.g., when the CSS colors of an element change).

For further insights, refer to the comprehensive guide on repaints and reflows: Repaints and Reflows: Manipulating the DOM responsibly.

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