Class Send

A message or packet to send to a specific node in the graph.

The Send class is used within a StateGraph's conditional edges to dynamically invoke a node with a custom state at the next step.

Importantly, the sent state can differ from the core graph's state, allowing for flexible and dynamic workflow management.

One such example is a "map-reduce" workflow where your graph invokes the same node multiple times in parallel with different states, before aggregating the results back into the main graph's state.

Example

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

const ChainState = Annotation.Root({
  subjects: Annotation<string[]>,
  jokes: Annotation<string[]>({
    reducer: (a, b) => a.concat(b),
  }),
});

const continueToJokes = async (state: typeof ChainState.State) => {
  return state.subjects.map((subject) => {
    return new Send("generate_joke", { subjects: [subject] });
  });
};

const graph = new StateGraph(ChainState)
  .addNode("generate_joke", (state) => ({
    jokes: [`Joke about ${state.subjects}`],
  }))
  .addConditionalEdges("__start__", continueToJokes)
  .addEdge("generate_joke", "__end__")
  .compile();

const res = await graph.invoke({ subjects: ["cats", "dogs"] });
console.log(res);

// Invoking with two subjects results in a generated joke for each
// { subjects: ["cats", "dogs"], jokes: [`Joke about cats`, `Joke about dogs`] }
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