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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.
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`] }