example.js

// Wite a Langchain js program that sends a prompt to the OpenAI LLM model and outputs the results to a stream in the process.stdout.
// Also use the dotenv module to load the API key from the .env file.
// We are using package.json type module to import the dotenv module.

import * as dotenv from 'dotenv';
dotenv.config();

import { ChatOpenAI } from '@langchain/openai';
import { ChatPromptTemplate } from '@langchain/core/prompts';
import { StringOutputParser } from '@langchain/core/output_parsers';

const prompt = ChatPromptTemplate.fromMessages([
    ["human", "What is the formula for converting Fahrenheit to Celsius?"]
]);
const model = new ChatOpenAI();
const outputParser = new StringOutputParser();

const chain = prompt.pipe(model).pipe(outputParser);

const stream = await chain.stream();

for await (const chunk of stream) {
    process.stdout.write(chunk, 'utf-8');
}