Stateful Applications Examples

import { StateGraph, MessagesAnnotation, START, END } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";
import { HumanMessage, AIMessage } from "@langchain/core/messages";
import { ChatOpenAI } from "@langchain/openai";

const model = new ChatOpenAI();

const chatNode = async (state: typeof MessagesAnnotation.State) => {
  const response = await model.invoke(state.messages);
  return { messages: [response] };
};

const chatbot = new StateGraph(MessagesAnnotation)
  .addNode("chat", chatNode)
  .addEdge(START, "chat")
  .addEdge("chat", END)
  .compile({ checkpointer: new MemorySaver() });

// First message
await chatbot.invoke(
  { messages: [new HumanMessage("Hi! My name is Alice.")] },
  { configurable: { thread_id: "user-123" } }
);

// Follow-up (remembers context)
const result = await chatbot.invoke(
  { messages: [new HumanMessage("What's my name?")] },
  { configurable: { thread_id: "user-123" } }
);
// Response: "Your name is Alice."

import { entrypoint, getPreviousState } from "@langchain/langgraph";
import { MemorySaver } from "@langchain/langgraph-checkpoint";

interface WorkflowState {
  stepsDone: string[];
  data: any;
}

const workflow = entrypoint({
  name: "multi-step",
  checkpointer: new MemorySaver()
}, async (input: { action: string; data?: any }) => {
  const prev = getPreviousState<WorkflowState>();

  const stepsDone = [...(prev?.stepsDone || []), input.action];
  const data = input.data || prev?.data;

  // Process based on action
  if (input.action === "start") {
    return entrypoint.final({
      value: "Started. Call with action 'process' next.",
      save: { stepsDone, data: input.data }
    });
  }

  if (input.action === "process") {
    const processed = processData(data);
    return entrypoint.final({
      value: "Processed. Call with action 'finish' next.",
      save: { stepsDone, data: processed }
    });
  }

  if (input.action === "finish") {
    return entrypoint.final({
      value: `Completed ${stepsDone.length} steps: ${stepsDone.join(", ")}`,
      save: { stepsDone, data }
    });
  }
});

const config = { configurable: { thread_id: "workflow-1" } };

await workflow.invoke({ action: "start", data: initialData }, config);
await workflow.invoke({ action: "process" }, config);
const result = await workflow.invoke({ action: "finish" }, config);