LLMChain

An LLMChain is the simplest type of chain, and is used widely in other chains, so understanding it is important.

An LLMChain consists of a PromptTemplate and an LLM.

We can construct an LLMChain which takes user input, formats it with a PromptTemplate, and then passes the formatted response to an LLM.

import { OpenAI } from "langchain/llms";
import { PromptTemplate } from "langchain/prompts";
const model = new OpenAI({ temperature: 0.9 });
const template = "What is a good name for a company that makes {product}?";
const prompt = new PromptTemplate({
  template: template,
  inputVariables: ["product"],
});

We can now create a very simple chain that will take user input, format the prompt with it, and then send it to the LLM:

import { LLMChain } from "langchain/chains";

const chain = new LLMChain({ llm: model, prompt: prompt });

Now we can run that chain only specifying the product!

const res = await chain.call({ product: "colorful socks" });
console.log({ res });

{ res: { text: '\n\nColorfulCo Sockery.' } }

LLMChain also supports output streaming by providing both the streaming: true parameter and the appropriate callbackManager.handleNewToken callback function. Note: OpenAI as of this writing does not support tokenUsage reporting while streaming is enabled.

const model = new OpenAI({
  streaming: true,
  callbackManager: CallbackManager.fromHandlers({
    handleLLMNewToken: (token: string) => console.log(token),
  },
});