Core Concepts

In the following part we will introduce you to the core concepts of React Flow and explain how to create an interactive flow. A flow consists of nodes and edges (or just nodes). You can pass arrays of nodes and edges as props to the ReactFlow component. Hereby all node and edge ids need to be unique. A node needs a position and a label (this could be different if you are using custom nodes) and an edge needs a source (node id) and a target (node id). You can read more about the options in the Node options and Edge options sections.

Controlled or Uncontrolled

With React Flow you have two ways to setup a flow. You can either create a controlled or an uncontrolled one. We recommend to use a controlled one but for simpler use cases you can also setup an uncontrolled flow. In the following part we will setup a controlled flow. Let’s start by adding some nodes and edges to the ReactFlow component:

export default function App() {
  const data: string = "world"

  return <h1>Hello {data}</h1>
}

Basic Functionality

By default React Flow doesn’t do any internal state updates besides handling the viewport when you setup a controlled flow. As with an <input /> component you need to pass handlers to apply the changes that are triggered by React Flow to your nodes and edges. In order to select, drag and remove nodes and edges you need to implement an onNodesChange and an onEdgesChange handler:

export default function App() {
  const data: string = "world"

  return <h1>Hello {data}</h1>
}

What is happening here? Whenever React Flow triggers a change (node init, node drag, edge select, etc.), the onNodesChange handler gets called. We export an applyNodeChanges handler so that you don’t need to handle the changes by yourself. The applyNodeChanges handler returns an updated array of nodes that is your new nodes array. You now have an interactive flow with the following kinds of interactions:

• selectable nodes and edges
• draggable nodes
• removable nodes and edges - (press Backspace to remove a selected node or edge, can be adjusted with the deleteKeyCode prop)
• multi-selection area by pressing Shift (that’s the default selectionKeyCode)
• multi-selection by pressing command (that’s the default multiSelectionKeyCode)

For convenience we export the helper hooks useNodesState and useEdgesState that you can use to create the nodes and edges state:

const [nodes, setNodes, onNodesChange] = useNodesState(initialNodes);
const [edges, setEdges, onEdgesChange] = useEdgesState(initialEdges);

Connecting Nodes

The last piece that is missing to get the full interactivity is the onConnect handler. You need to implement it, in order to handle new connections.

export default function App() {
  const data: string = "world"

  return <h1>Hello {data}</h1>
}

In this example we are using the addEdge handler that returns an array of edges with the newly created one. If you want to set a certain edge option whenever an edge gets created you pass your options like this:

const onConnect = useCallback(
  (connection) =>
    setEdges((eds) => addEdge({ ...connection, animated: true }, eds)),
  [setEdges],
);

or use the defaultEdgeOptions prop:

const defaultEdgeOptions = { animated: true };
...
<ReactFlow
  nodes={nodes}
  edges={edges}
  onNodesChange={onNodesChange}
  onEdgesChange={onEdgesChange}
  onConnect={onConnect}
  defaultEdgeOptions={defaultEdgeOptions}
/>;