Messages

import {
  BaseMessage,
  HumanMessage,
  AIMessage,
  SystemMessage,
  ToolMessage
} from "@langchain/core/messages";

const message = new HumanMessage("Hello, how are you?");

// With additional fields
const message = new HumanMessage({
  content: "Hello",
  name: "Alice",
  additional_kwargs: { userId: "123" }
});

const message = new AIMessage("I'm doing well, thank you!");

// With tool calls
const message = new AIMessage({
  content: "",
  tool_calls: [{
    name: "calculator",
    args: { expression: "2+2" },
    id: "call_123"
  }]
});

const message = new SystemMessage(
  "You are a helpful assistant that speaks like a pirate."
);

const message = new ToolMessage({
  content: "4",
  tool_call_id: "call_123",
  name: "calculator"
});

import { HumanMessage } from "@langchain/core/messages";

const message = new HumanMessage({
  content: [
    {
      type: "text",
      text: "What's in this image?"
    },
    {
      type: "image_url",
      image_url: { url: "https://example.com/image.jpg" }
    }
  ]
});

import { ChatOpenAI } from "@langchain/openai";

const model = new ChatOpenAI();

const response = await model.invoke([
  ["system", "You are a helpful assistant"],
  ["human", "Hello!"]
]);

import { filterMessages } from "@langchain/core/messages";

const filtered = filterMessages(messages, {
  includeTypes: ["human", "ai"],
  excludeNames: ["system"]
});

import { trimMessages } from "@langchain/core/messages";

const trimmed = await trimMessages(messages, {
  maxTokens: 1000,
  strategy: "last", // or "first"
  tokenCounter: (messages) => messages.length * 10
});

const aiMessage = new AIMessage({
  content: "Let me calculate that for you.",
  tool_calls: [
    {
      name: "calculator",
      args: { expression: "100 * 25" },
      id: "call_abc123",
      type: "tool_call"
    }
  ]
});

// Check for tool calls
if (aiMessage.tool_calls && aiMessage.tool_calls.length > 0) {
  console.log("Model wants to call tools:", aiMessage.tool_calls);
}

import { HumanMessage, AIMessage } from "@langchain/core/messages";

const conversation = [
  new HumanMessage("Hi, my name is Alice"),
  new AIMessage("Hello Alice! How can I help you today?"),
  new HumanMessage("What's my name?"),
];

const response = await model.invoke(conversation);
// "Your name is Alice."

const messages = [
  new HumanMessage("What's 25 * 4?"),
  new AIMessage({
    content: "",
    tool_calls: [{
      name: "calculator",
      args: { expression: "25*4" },
      id: "call_1"
    }]
  }),
  new ToolMessage({
    content: "100",
    tool_call_id: "call_1"
  }),
  new AIMessage("25 * 4 = 100")
];