Events and Callbacks

Core Chart callbacks run in Python through a live notebook widget or framework transport. Browser interactions continue to work in standalone HTML, but a self-contained file has no Python process to call.

Supplying a callback enables its corresponding browser interaction. Callback payload details are still experimental during the alpha series.

Hover and click rows contain trace, canonical index, x, y, x_kind, and y_kind. Depending on the mark's channels, they can also contain color_value, color_category, or size_value. These are data dictionaries, not DOM event objects or formatted tooltip strings.

Selection exposes:

• per_trace — {trace_id: numpy_uint32_indices} in canonical row space.
• index — all selected indices concatenated; use per_trace when trace identity matters.
• xy(trace_id=0) — canonical f64 x/y arrays for one selected trace.
• len(selection) — total selected rows across traces.

Clearing selection delivers an empty Selection. Chart.select_range() returns the same type without requiring a browser gesture.

The client dispatches bubbling custom events from the chart root:

A live hover can emit an immediate resident readout followed by an exact update. Consumers that only need the canonical Python row should use on_hover.

The separate reflex-xy adapter intentionally uses semantic component props: on_point_hover, on_point_click, on_select_end, and on_view_change. Those are adapter props, not aliases accepted by core Chart. See the Reflex integration for state-backed payloads. on_select_end includes total, cleared, and either box bounds or the data-space polygon used by a lasso selection.

Linked charts broadcast viewport ranges only. They do not automatically link selection state or cross-filter data.