Advanced React Flow Patterns

Gates (check before shipping)

Use these as sequenced checks—not “I think it works.”

1. Sub-flows / groups: Pass: Every parentId matches an existing node id; the parent type is registered in nodeTypes; child positions are relative to the parent as intended (spot-check one drag inside/outside the group).
2. Custom connection line: Pass: With a valid/invalid drag, stroke or connectionStatus visibly differs; path renders without console errors from getSmoothStepPath (invalid coords).
3. External drag-and-drop: Pass: onDragOver always preventDefault(); drop position uses screenToFlowPosition (not raw clientX/clientY as flow coords); new node appears under the cursor on the pane.
4. Undo/redo: Pass: One undo returns to the prior { nodes, edges }; redo restores; rapid changes do not leave canUndo/canRedo inconsistent with visible graph (exercise add → undo → redo once).
5. Programmatic layout (dagre): Pass: After setNodes, node positions match intended rankdir; fitView runs after layout (e.g. requestAnimationFrame) so the viewport is not stale.
6. Connect on drop (new node): Pass: Dropping on empty pane creates a node and an edge from the source handle; dropping on a valid target does not duplicate nodes (only the invalid-drop path adds a node).
7. Selectors / store: Pass: Components that useStore with objects use shallow (or equivalent) so unrelated store updates do not re-render every frame.

Sub-Flows (Nested Nodes)