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*   In Memory Store

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In Memory Store
===============

This example demonstrates how to setup chat history storage using the `InMemoryStore` KV store integration.

Usage[​](#usage "Direct link to Usage")
---------------------------------------

The `InMemoryStore` allows for a generic type to be assigned to the values in the store. We'll assign type `BaseMessage` as the type of our values, keeping with the theme of a chat history store.

    import { InMemoryStore } from "langchain/storage/in_memory";import { AIMessage, BaseMessage, HumanMessage } from "@langchain/core/messages";// Instantiate the store using the `fromPath` method.const store = new InMemoryStore<BaseMessage>();/** * Here you would define your LLM and chat chain, call * the LLM and eventually get a list of messages. * For this example, we'll assume we already have a list. */const messages = Array.from({ length: 5 }).map((_, index) => {  if (index % 2 === 0) {    return new AIMessage("ai stuff...");  }  return new HumanMessage("human stuff...");});// Set your messages in the store// The key will be prefixed with `message:id:` and end// with the index.await store.mset(  messages.map((message, index) => [`message:id:${index}`, message]));// Now you can get your messages from the storeconst retrievedMessages = await store.mget(["message:id:0", "message:id:1"]);console.log(retrievedMessages.map((v) => v));/**[  AIMessage {    lc_kwargs: { content: 'ai stuff...', additional_kwargs: {} },    content: 'ai stuff...',    ...  },  HumanMessage {    lc_kwargs: { content: 'human stuff...', additional_kwargs: {} },    content: 'human stuff...',    ...  }] */// Or, if you want to get back all the keys you can call// the `yieldKeys` method.// Optionally, you can pass a key prefix to only get back// keys which match that prefix.const yieldedKeys = [];for await (const key of store.yieldKeys("message:id:")) {  yieldedKeys.push(key);}// The keys are not encoded, so no decoding is necessaryconsole.log(yieldedKeys);/**[  'message:id:0',  'message:id:1',  'message:id:2',  'message:id:3',  'message:id:4'] */// Finally, let's delete the keys from the storeawait store.mdelete(yieldedKeys);

#### API Reference:

*   [InMemoryStore](https://api.js.langchain.com/classes/langchain_core_stores.InMemoryStore.html) from `langchain/storage/in_memory`
*   [AIMessage](https://api.js.langchain.com/classes/langchain_core_messages.AIMessage.html) from `@langchain/core/messages`
*   [BaseMessage](https://api.js.langchain.com/classes/langchain_core_messages.BaseMessage.html) from `@langchain/core/messages`
*   [HumanMessage](https://api.js.langchain.com/classes/langchain_core_messages.HumanMessage.html) from `@langchain/core/messages`

* * *

#### Help us out by providing feedback on this documentation page:

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