core[docs]: Docs & example for runnable history

docs/core_docs/docs/expression_language/cookbook/with_history.mdx

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+import CodeBlock from "@theme/CodeBlock";
+import Example from "@examples/guides/expression_language/runnable_history.ts";
+
+# Runnables With History
+
+<CodeBlock language="typescript">{Example}</CodeBlock>

examples/src/guides/expression_language/runnable_history.ts

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+import { ChatOpenAI } from "langchain/chat_models/openai";
+import { ChatMessageHistory } from "langchain/memory";
+import { ChatPromptTemplate } from "langchain/prompts";
+import {
+  RunnableConfig,
+  RunnableSequence,
+  RunnableWithMessageHistory,
+} from "langchain/runnables";
+import {
+  BaseListChatMessageHistory,
+  BaseMessage,
+  HumanMessage,
+} from "langchain/schema";
+import { StringOutputParser } from "langchain/schema/output_parser";
+
+// Define your session history store.
+// This is where you will store your chat history, keyed by sessionId.
+async function getListSessionHistory(): Promise<
+  (sessionId: string) => Promise<BaseListChatMessageHistory>
+> {
+  const chatHistoryStore: { [key: string]: BaseListChatMessageHistory } = {};
+
+  async function getSessionHistory(
+    sessionId: string
+  ): Promise<BaseListChatMessageHistory> {
+    if (!(sessionId in chatHistoryStore)) {
+      chatHistoryStore[sessionId] = new ChatMessageHistory();
+    }
+    return chatHistoryStore[sessionId];
+  }
+
+  return getSessionHistory;
+}
+
+// Instantiate your model and prompt.
+const model = new ChatOpenAI({});
+const prompt = ChatPromptTemplate.fromMessages([
+  ["ai", "You are a helpful assistant."],
+  ["human", "{question}"],
+]);
+
+// Create a simple runnable which passes a question to the AI.
+const runnable = RunnableSequence.from([
+  {
+    question: (messages: Array<BaseMessage>) =>
+      messages.map((m) => `${m._getType()}: ${m.content}`).join("\n"),
+  },
+  prompt,
+  model,
+  new StringOutputParser(),
+]);
+
+// Create your `RunnableWithMessageHistory` object, passing in the
+// runnable created above.
+const withHistory = new RunnableWithMessageHistory({
+  runnable,
+  config: {},
+  getMessageHistory: await getListSessionHistory(),
+});
+
+// Create your `configurable` object. This is where you pass in the
+// `sessionId` which is used to identify chat sessions in your message store.
+const config: RunnableConfig = { configurable: { sessionId: "1" } };
+
+// Pass in your question as an instance of HumanMessage.
+// This is because in our runnable, we prefix each message
+// with the type.
+let output = await withHistory.invoke(
+  [new HumanMessage("Hello there, I'm Archibald!")],
+  config
+);
+console.log("output 1:", output);
+/**
+ * output 1: AI: Hello Archibald! How can I assist you today?
+ */
+
+output = await withHistory.invoke(
+  [new HumanMessage("What's my name?")],
+  config
+);
+console.log("output 2:", output);
+/**
+ * output 2: AI: Your name is Archibald, as you mentioned earlier. Is there anything else I can help you with?
+ */
+
+/**
+ * You can see the LangSmith traces here:
+ * output 1 @link https://smith.langchain.com/public/f8baefdb-4dd4-4e58-abb3-bbd91da2b543/r
+ * output 2 @link https://smith.langchain.com/public/df49265e-b1db-4f43-a47d-f362310bd01f/r
+ */