Reactflow Expert

ReactFlow Expert

Builds DAG visualizations using ReactFlow v12 with custom agent nodes, ELKjs auto-layout, Zustand state management, and live execution state updates.

Decision Points

State Management Strategy Selection

Graph Size <= 50 nodes?
├─ YES: Use useNodesState/useEdgesState hooks (simpler)
└─ NO: Use Zustand store
    ├─ Real-time updates required? → Include WebSocket integration
    ├─ Multi-component access? → Global Zustand store
    └─ Complex interactions? → Add action methods (updateNodeData, bulkUpdate)

Layout Algorithm by DAG Shape

Node Count:
├─ < 20 nodes: Use 'layered' algorithm with direction='DOWN'
├─ 20-100 nodes: Use 'layered' with direction='RIGHT' 
├─ > 100 nodes: Use 'stress' algorithm (better for large graphs)
└─ Highly connected (edges > 2x nodes): Use 'force' algorithm

Aspect Ratio:
├─ Wide dashboard: direction='RIGHT'
├─ Tall sidebar: direction='DOWN' 
└─ Square viewport: Let ELK choose optimal direction

Custom Node Complexity Decision

Node Data Fields:
├─ Only status + name: Use built-in node types with custom styling
├─ 3-5 fields: Custom node with simple layout
├─ 6+ fields or nested data: Custom node with collapsible sections
└─ Interactive elements: Custom node + "nodrag" className on controls

Sync Strategy for Live Updates

Update Frequency:
├─ Real-time (< 1s): WebSocket with optimistic updates
├─ Frequent (1-10s): WebSocket with batching
├─ Periodic (> 10s): HTTP polling
└─ User-triggered: Manual refresh button

Data Size:
├─ Full DAG < 1MB: Send complete state
├─ Large DAG: Send delta updates (node ID + changed fields)
└─ Huge DAG: Implement viewport-based loading

Failure Modes

Infinite Re-render Loop

Symptom: Browser tab freezes, React DevTools shows constant re-renders Detection: If nodeTypes object is defined inside component body Fix: Move nodeTypes outside component or wrap in useMemo

Stale State Updates

Symptom: Node status changes don't appear visually, but store updates correctly Detection: If mutating existing node objects instead of creating new ones Fix: Always spread objects: { ...node, data: { ...node.data, newField } }

Layout Thrashing

Symptom: Nodes jump around constantly, poor performance with live updates Detection: If ELK layout runs on every state change instead of topology changes Fix: Only trigger layout when nodes/edges are added/removed, not data updates

Handle Positioning Mismatch

Symptom: Edges connect to wrong positions or don't connect at all Detection: If using v11 position properties (xPos, yPos) in v12 Fix: Update to v12 properties: positionAbsoluteX, positionAbsoluteY

Drag Interference

Symptom: Buttons/inputs inside custom nodes trigger node dragging Detection: If interactive elements don't have proper event handling Fix: Add className="nodrag" to all buttons, inputs, selects inside nodes

Worked Examples

Complete WebSocket DAG Sync → ELK Layout → Custom Node Render

Scenario: Build a live workflow dashboard showing agent execution status

Step 1: Setup Zustand Store with WebSocket Integration

const useDAGStore = create<DAGStore>((set, get) => ({
  nodes: [],
  edges: [],
  onNodesChange: (changes) => set({ nodes: applyNodeChanges(changes, get().nodes) }),
  onEdgesChange: (changes) => set({ edges: applyEdgeChanges(changes, get().edges) }),
  updateNodeData: (nodeId, data) => {
    // EXPERT MOVE: Create new object to trigger React re-render
    set({
      nodes: get().nodes.map((n) =>
        n.id === nodeId ? { ...n, data: { ...n.data, ...data } } : n
      ),
    });
  },
}));

Step 2: WebSocket Handler (Novice Miss: Updating in place)

function useDAGStream(dagId: string) {
  const updateNodeData = useDAGStore((s) => s.updateNodeData);
  
  useEffect(() => {
    const ws = new WebSocket(`ws://api/dag/${dagId}/stream`);
    ws.onmessage = (event) => {
      const update = JSON.parse(event.data);
      if (update.type === 'node_status') {
        // EXPERT: Only update data, don't re-layout
        updateNodeData(update.nodeId, { 
          status: update.status, 
          metrics: update.metrics 
        });
      } else if (update.type === 'topology_change') {
        // EXPERT: Only NOW do we re-layout
        triggerLayout();
      }
    };
  }, [dagId, updateNodeData]);
}

Step 3: ELK Layout with Performance Optimization

const useAutoLayout = () => {
  const { fitView } = useReactFlow();
  const { nodes, edges, setNodes } = useDAGStore();
  
  return useCallback(async (direction = 'DOWN') => {
    // EXPERT: Check node count and choose algorithm
    const algorithm = nodes.length > 100 ? 'stress' : 'layered';
    
    const layouted = await elk.layout({
      id: 'root',
      layoutOptions: {
        'elk.algorithm': algorithm,
        'elk.direction': direction,
        'elk.spacing.nodeNode': nodes.length > 50 ? '60' : '80',
      },
      children: nodes.map((n) => ({
        ...n,
        // EXPERT: Pass measured dimensions to prevent layout jumps
        width: n.measured?.width ?? 220,
        height: n.measured?.height ?? 120,
      })),
      edges,
    });
    
    const positioned = layouted.children!.map((elkN) => ({
      ...nodes.find((n) => n.id === elkN.id)!,
      position: { x: elkN.x!, y: elkN.y! },
    }));
    
    setNodes(positioned);
    // EXPERT: Defer fitView until after DOM update
    requestAnimationFrame(() => fitView());
  }, [nodes, edges, setNodes, fitView]);
};

Step 4: Custom Agent Node with Status Colors

// EXPERT: Define outside component to prevent re-registration
const nodeTypes = { agentNode: AgentNode };

function AgentNode({ data }: NodeProps) {
  return (
    <div className={`agent-node status-${data.status}`}>
      <Handle type="target" position={Position.Top} />
      <div className="node-header">
        <span className={`status-dot ${data.status}`} />
        <span>{data.role}</span>
      </div>
      {data.status === 'running' && data.progress && (
        <div className="progress-bar">
          <div style={{ width: `${data.progress}%` }} />
        </div>
      )}
      {/* EXPERT: Interactive elements need nodrag */}
      <button className="nodrag" => pauseAgent(data.id)}>
        Pause
      </button>
      <Handle type="source" position={Position.Bottom} />
    </div>
  );
}

Performance Tradeoffs Demonstrated:

• Zustand vs useState: Zustand handles 100+ node updates without re-rendering parent
• ELK algorithm choice: 'layered' fast for < 100 nodes, 'stress' for larger graphs
• WebSocket batching: Group status updates to avoid layout thrashing

Quality Gates

Functional Validation

• ReactFlow component renders without console errors
• All custom node types appear in nodeTypes registry
• ELK layout completes within 2 seconds for target node count
• WebSocket connections establish and receive test messages
• Node data updates trigger visual changes within 200ms

Performance Thresholds

• Initial render completes within 1 second for 50 nodes
• Layout computation finishes within 3 seconds for 100 nodes
• Memory usage stays under 100MB for 200-node graphs
• Frame rate maintains 30fps during zoom/pan operations
• WebSocket updates don't cause visible stuttering

Visual Quality Checks

• Edges connect to correct handle positions (not node centers)
• Node labels remain readable at 50% zoom level
• Status colors match design system specifications
• Interactive elements (buttons, inputs) don't trigger node dragging
• fitView() centers graph with appropriate padding margins

Accessibility Requirements

• All interactive nodes have proper ARIA labels
• Keyboard navigation works for node selection
• Color-based status indicators have text/icon alternatives
• Focus indicators visible on custom node components
• Screen reader announces node status changes

NOT-FOR Boundaries

Static Diagrams: For Mermaid flowcharts or architectural diagrams, use mermaid-graph-writer instead. ReactFlow is for interactive, live-updating visualizations.

Simple Charts: For bar charts, line graphs, or pie charts, use dedicated charting libraries (recharts, d3) instead. ReactFlow is specifically for node-edge graphs.

General React Development: For standard React components, forms, or layouts, use general React skills instead. This skill is ReactFlow-specific.

3D Visualizations: For 3D network graphs or spatial layouts, use three.js or WebGL libraries instead. ReactFlow is 2D-only.

Mobile-First Apps: For touch-first mobile interfaces, consider native gestures instead. ReactFlow is optimized for mouse/trackpad interaction.

Real-time Collaboration: For multi-user editing like Figma, use specialized real-time sync libraries instead. ReactFlow handles read-only live updates well but not collaborative editing.