[bvaughn]

• useDynamicRowHeight stores all of the rows measured at once (e.g. a newly visible page of rows) in a single update, rather than copying its cache for each row.
• Lists with dynamic row heights keep the rows on screen in place when rows above them change height, e.g. as rows are measured while scrolling up (such as through a chat log), or when a row's content resizes. The scroll position is adjusted in the same frame, so rows never visibly jump. It isn't adjusted while the list is scrolled to the end or while scrollToRow is scrolling. While the user is touch scrolling, the rows are shifted instead (iOS ignores changes to the scroll position during touch scrolling), and the scroll position is adjusted once scrolling stops.
• With dynamic row heights and a rowKey (or useVirtualizer's new getItemKey option), measured heights are stored by key, so they follow their rows when rows are inserted, removed, or reordered; and the rows on screen stay in place when rows are inserted or removed above them, e.g. when older messages are loaded at the top of a chat (including while scrolled to the top or end of the list), or when the data is filtered or re-sorted (as long as a row in view is still in the list). Apps that adjusted the scroll position themselves after inserting rows should stop doing so when they pass a key. Without a key, heights are stored by index as before. DynamicRowHeight's getRowHeight and setRowHeight methods accept an optional key, and observeRowElements the list's rows ({ count, getKey }); custom implementations that ignore them keep working (by index). Heights of rows that are no longer in the list are removed once the cache holds more than twice as many rows as the list has had (and at least 1,000), so rows hidden for a while (e.g. by a filter) keep their heights. The RowKeys type is exported for custom DynamicRowHeight implementations. Keys must be stable (not the index or a random value), and the function should be cheap, since it's called for many rows.
• Add anchorRow method to the List imperative API (and anchorItem to useVirtualizer) for keeping a specific row where it is on screen while its height changes, e.g. when the user expands or collapses it. Call it before making the change; the row is kept in place for the specified duration (1 second by default). (By default, the list keeps the first visible row that didn't change height in place, so a row at the top of the viewport that grows would extend upward.)

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Project	Deployment	Actions	Updated
react-window	Ready	Preview	Oct 29, 2026 12:39am UTC