Question

What does DOM reflow occur?

Answer 1

Reflow is the name of the web browser process for re-calculating the positions and geometries of elements in the document, for the purpose of re-rendering part or all of the document. 

Reflow occurs when:

1. Insert, remove or update an element in the DOM.
2. Modify content on the page, e.g. the text in an input box.
3. Move a DOM element.
4. Animate a DOM element.
5. Take measurements of an element such as offsetHeight or getComputedStyle.
6. Change a CSS style.