createReactAgent

import { ChatOpenAI } from "@langchain/openai";
import { tool } from "@langchain/core/tools";
import { z } from "zod";
import { createReactAgent } from "@langchain/langgraph/prebuilt";

const model = new ChatOpenAI({
  model: "gpt-4o",
});

const getWeather = tool((input) => {
  if (["sf", "san francisco"].includes(input.location.toLowerCase())) {
    return "It's 60 degrees and foggy.";
  } else {
    return "It's 90 degrees and sunny.";
  }
}, {
  name: "get_weather",
  description: "Call to get the current weather.",
  schema: z.object({
    location: z.string().describe("Location to get the weather for."),
  })
})

const agent = createReactAgent({ llm: model, tools: [getWeather] });

const inputs = {
  messages: [{ role: "user", content: "what is the weather in SF?" }],
};

const stream = await agent.stream(inputs, { streamMode: "values" });

for await (const { messages } of stream) {
  console.log(messages);
}
// Returns the messages in the state at each step of execution