Class Command<R>

One or more commands to update the graph's state and send messages to nodes. Can be used to combine routing logic with state updates in lieu of conditional edges

Example

import { Annotation, Command } from "@langchain/langgraph";

// Define graph state
const StateAnnotation = Annotation.Root({
  foo: Annotation<string>,
});

// Define the nodes
const nodeA = async (_state: typeof StateAnnotation.State) => {
  console.log("Called A");
  // this is a replacement for a real conditional edge function
  const goto = Math.random() > .5 ? "nodeB" : "nodeC";
  // note how Command allows you to BOTH update the graph state AND route to the next node
  return new Command({
    // this is the state update
    update: {
      foo: "a",
    },
    // this is a replacement for an edge
    goto,
  });
};

// Nodes B and C are unchanged
const nodeB = async (state: typeof StateAnnotation.State) => {
  console.log("Called B");
  return {
    foo: state.foo + "|b",
  };
}

const nodeC = async (state: typeof StateAnnotation.State) => {
  console.log("Called C");
  return {
    foo: state.foo + "|c",
  };
}

import { StateGraph } from "@langchain/langgraph";

// NOTE: there are no edges between nodes A, B and C!
const graph = new StateGraph(StateAnnotation)
  .addNode("nodeA", nodeA, {
    ends: ["nodeB", "nodeC"],
  })
  .addNode("nodeB", nodeB)
  .addNode("nodeC", nodeC)
  .addEdge("__start__", "nodeA")
  .compile();

await graph.invoke({ foo: "" });

// Randomly oscillates between
// { foo: 'a|c' } and { foo: 'a|b' }
Copy