Example: Langfuse Prompt Management with Langchain (JS)

const langfuseParams = {
    publicKey: "",
    secretKey: "",
    baseUrl: "https://cloud.langfuse.com",
    flushAt: 1 // cookbook-only, send all events immediately
}

import { Langfuse } from "npm:langfuse"
const langfuse = new Langfuse(langfuseParams)

const prompt =  await langfuse.createPrompt({
    name: "jokes",
    prompt: "Tell me a joke about {{topic}}",
    config: {
      modelName: "gpt-4",
      temperature: 1,
    }, // optionally, add configs (e.g. model parameters or model tools)
    labels: ["production"] // directly promote to production
});

const prompt = await langfuse.getPrompt("jokes")

prompt.prompt

"Tell me a joke about {{topic}}"

prompt.config

{ modelName: [32m"gpt-4", temperature: 1 }

import { PromptTemplate } from "npm:@langchain/core/prompts"
 
const promptTemplate = PromptTemplate.fromTemplate(
    prompt.getLangchainPrompt()
  ).withConfig({
    metadata: { langfusePrompt: prompt }
  });

import { CallbackHandler } from "npm:langfuse-langchain"
const langfuseLangchainHandler = new CallbackHandler(langfuseParams)

import { ChatOpenAI } from "npm:@langchain/openai"
import { RunnableSequence } from "npm:@langchain/core/runnables";
 
const model = new ChatOpenAI({
    modelName: prompt.config.modelName,
    temperature: prompt.config.temperature
});
const chain = RunnableSequence.from([promptTemplate, model]);

const res = await chain.invoke(
    { topic: "Europe and the Americas" },
    { callbacks: [langfuseLangchainHandler] }
);

const prompt =  await langfuse.createPrompt({
    name: "extractor",
    prompt: "Extracts fields from the input.",
    config: {
      modelName: "gpt-4",
      temperature: 0,
      schema: {
        type: "object",
        properties: {
          tone: {
            type: "string",
            enum: ["positive", "negative"],
            description: "The overall tone of the input",
          },
          word_count: {
            type: "number",
            description: "The number of words in the input",
          },
          chat_response: {
            type: "string",
            description: "A response to the human's input",
          },
        },
        required: ["tone", "word_count", "chat_response"],
      }
    }, // optionally, add configs (e.g. model parameters or model tools)
    labels: ["production"] // directly promote to production
});

const extractorPrompt = await langfuse.getPrompt("extractor")

const extractionFunctionSchema = {
    name: "extractor",
    description: prompt.prompt,
    parameters: prompt.config.schema,
}

import { ChatOpenAI } from "npm:@langchain/openai";
import { JsonOutputFunctionsParser } from "npm:langchain/output_parsers";
 
// Instantiate the parser
const parser = new JsonOutputFunctionsParser();
 
// Instantiate the ChatOpenAI class
const model = new ChatOpenAI({ 
    modelName: prompt.config.modelName,
    temperature: prompt.config.temperature
});
 
// Create a new runnable, bind the function to the model, and pipe the output through the parser
const runnable = model
  .bind({
    functions: [extractionFunctionSchema],
    function_call: { name: "extractor" },
  })
  .pipe(parser);

import { HumanMessage } from "npm:@langchain/core/messages";
 
// Invoke the runnable with an input
const result = await runnable.invoke(
    [new HumanMessage("What a beautiful day!")],
    { callbacks: [langfuseLangchainHandler] }
);