Events

const off = chart.on('nodeClick', ({ id, item }) => {
  console.log(id, item)
})
// later
off()

Event	Payload	When
ready	—	The first frame has been drawn.
nodeClick	{ id, item }	A tap on a node. Not fired for a tap that lands on a card's own button or input.
nodeDblClick	{ id, item }	Two taps on the same node inside 300ms. The second does not also emit nodeClick.
nodeHover	{ id, item } or { id: null, item: null }	Enter and leave. Not re-fired for repeated moves within the same node.
toggle	{ id, open }	A node was expanded or collapsed, however it happened.
selectionChange	{ ids, items }	The selection changed. Carries the whole selection, not a delta.
nodeDrop	NodeDropEvent	A node was dropped somewhere new. Fires BEFORE anything moves.
addRequested	{ afterId, parentId, index }	The viewer pressed Shift+Enter on a node and wants a sibling after it. A request, not an action — see Without a pointer.
viewChange	ChartView	Camera, open branches, selection, highlight, isolation, filter or lifted caps changed. The whole view, exactly what getView() returns.
filterChange	{ query, matched }	The filter changed. matched is what filter() returns; query is null for none and for a predicate, which cannot be written down.
layoutChange	{ settings }	The layout or one of its knobs changed. Carries the settings as they now stand, not the delta — so a sidebar mirroring the chart reads what IS.
childrenLoaded	{ id, item, items }	loadChildren returned and the chart took the children in. Informational — it holds them either way.
viewportChange	{ camera }	Any camera change — pan, zoom, ease, kinetic coast. Fires per frame while one is running.
warning	Warning	Something in the data could not be honoured.

Refusing a move

nodeDrop is the one event that fires before the thing it describes. That is what makes it refusable:

chart.on('nodeDrop', ({ ids, parentId, index, mode, preventDefault }) => {
  if (parentId === null) return preventDefault() // no new roots
  save(ids, parentId, index)
})

Field
ids	What is moving, in tree order — the whole selection if a selected node was dragged
items	The same nodes' data objects
parentId	The new parent, or null for a drop that makes a root
index	Position among the new parent's children
mode	'into', 'before' or 'after'
preventDefault()	Refuse the move; the chart applies nothing

Without a preventDefault(), the chart applies the move as soon as the handler returns and animates the result — so an async handler must call it first, before its first await. NodeDropEvent is exported from every package. See Drag and drop.

Warnings are not errors

Bad data draws. A parentId naming nothing, a duplicate id, a cycle — each one is resolved in a defined way and reported rather than thrown:

chart.on('warning', ({ code, detail, ids }) => {
  console.warn(code, detail, ids)
})

code
duplicate-id	Two rows share an id. The later one is dropped.
orphan-parent	A parentId names nothing. The node becomes a root.
cycle	A node is its own ancestor. The link that closes the loop is cut.
load-failed	A loadChildren rejected. The node stays unloaded and the next click retries.

A tree is usually built from data somebody else owns, and refusing to render because one row of ten thousand points at a deleted manager is not useful behaviour. The chart shows you the other 9,999 and tells you about the one. load-failed is the odd one out — nothing is wrong with your data, a request did not come back — but it reaches you the same way for the same reason.

Warnings from the initial load are emitted after construction returns, so a listener attached on the next line still hears them.