The context object passed to middleware execute functions. Provides access to the current state, helper functions, and configuration.

Example

const middleware: Middleware = {
  name: 'validation',
  execute: (context, next, cancel) => {
    // Check if any nodes were added
    if (context.helpers.anyNodesAdded()) {
      console.log('Nodes added:', context.state.nodes);
    }

    // Access configuration
    console.log('Cell size:', context.config.background.cellSize);

    // Check what actions triggered this (supports transactions with multiple actions)
    if (context.modelActionTypes.includes('addNodes')) {
      // Validate new nodes
      const isValid = validateNodes(context.state.nodes);
      if (!isValid) {
        cancel(); // Block the operation
        return;
      }
    }

    next(); // Continue to next middleware
  }
};

Properties

actionStateManager

actionStateManager: ActionStateManager

Manager for action states (resizing, linking, etc.)

---

config

config: FlowConfig

The current diagram configuration

---

edgeRoutingManager

edgeRoutingManager: EdgeRoutingManager

Manager for edge routing algorithms

---

edgesMap

edgesMap: Map<string, Edge<object>>

Map for quick edge lookup by ID. Contains the current state after previous middleware processing. Use this to access edges by ID instead of iterating through state.edges.

---

environment

environment: EnvironmentInfo

Environment information (browser, rendering engine, etc.)

---

helpers

helpers: MiddlewareHelpers

Helper functions to check what changed (tracks all cumulative changes from the initial action and all previous middlewares)

---

history

history: MiddlewareHistoryUpdate[]

All state updates from previous middlewares in the chain

---

initialEdgesMap

initialEdgesMap: Map<string, Edge<object>>

The initial edges map before any modifications (before the initial action and before any middleware modifications). Use this to compare state before and after all modifications. Common usage: Access removed edge instances that no longer exist in edgesMap.

---

initialNodesMap

initialNodesMap: Map<string, Node>

The initial nodes map before any modifications (before the initial action and before any middleware modifications). Use this to compare state before and after all modifications. Common usage: Access removed node instances that no longer exist in nodesMap.

---

initialState

initialState: FlowState

The state before any modifications (before the initial action and before any middleware modifications)

---

initialUpdate

initialUpdate: FlowStateUpdate

The initial state update that triggered the middleware chain. Middlewares can add their own updates to the state, so this may not contain all modifications that will be applied. Use helpers to get actual knowledge about all changes.

---

modelActionType

modelActionType: ModelActionType

The action that triggered the middleware execution.

Deprecated

Use modelActionTypes instead, which supports multiple actions from transactions. For single actions, this returns the first (and only) action type.

---

modelActionTypes

modelActionTypes: ModelActionTypes

All action types that triggered the middleware execution. For transactions, this contains the transaction name followed by all action types from commands executed within the transaction. For single commands outside transactions, this is a single-element array.

Example

// For a transaction named 'batchUpdate' with addNodes and moveViewport commands:
// modelActionTypes = ['batchUpdate', 'addNodes', 'moveViewport']

// For a single command outside a transaction:
// modelActionTypes = ['addNodes']

Since

0.9.0

---

nodesMap

nodesMap: Map<string, Node>

Map for quick node lookup by ID. Contains the current state after previous middleware processing. Use this to access nodes by ID instead of iterating through state.nodes.

---

state

state: FlowState

The current state (includes the initial modification and all changes from previous middlewares)