Layout thrashing là gì? Cách tránh?

Đọc layout property (offsetHeight) rồi ngay lập tức ghi style → browser phải recalculate layout liên tục.

Tránh bằng: batch reads trước writes, dùng transform thay top/left, dùng requestAnimationFrame.

Reading a layout property (like offsetHeight) immediately followed by writing a style forces the browser to repeatedly recalculate layout.

Avoid it by: batching all reads before writes, using transform instead of top/left, and using requestAnimationFrame.