Callbacks

Every function prop TreeKit calls, and exactly when.

Prop	Type	Default	Description
onExpandedChange	(ids: string[]) => void	—	Any time the expanded set changes — expand, collapse, or a keyboard-driven toggle.
onNodeExpand	(node) => void	—	Once, specifically when node transitions collapsed → expanded.
onNodeCollapse	(node) => void	—	Once, specifically when node transitions expanded → collapsed.
onCheckedChange	(ids: string[], meta: { node }) => void	—	Any time the checked set changes. meta.node is whichever node the user directly toggled (cascaded descendants/ancestors aren't individually reported).
onSelectionChange	(ids: string[], meta: { node }) => void	—	Any time the active/highlighted selection changes (selectionMode !== "none").
onNodeClick	(node, event) => void	—	Every row click, regardless of selectionMode or showCheckboxes — checkbox clicks are excluded (they stopPropagation).
onNodeDoubleClick	(node, event) => void	—	Every row double-click.
onKeyDown	(event) => void	—	Fires after TreeKit's own arrow/space/enter/home/end handling has run, so you can layer additional shortcuts without fighting built-in navigation.
onLoadChildren	(node) => Promise<TreeNode[]>	—	Called once per node, the first time it's expanded while lazily-loadable — see Async Loading.
filterFn	(node, searchValue) => boolean	—	Called for every node on every searchValue change — not technically an event callback, but worth knowing it re-runs on every keystroke unless you debounce searchValue yourself.

Every callback is optional. TreeKit works fully uncontrolled with none of them provided — pass only the ones relevant to what your app needs to know.