npm install langchain
npm install @langchain/google-vertexai

const configuration = {
  vertexAI: {
    credentials: {
      type: 'service_account',
      project_id: 'langchain-gemini-418916', (1)
      private_key_id: '6748041cc07c6e83cdd3001fa83301eb5abc8795',
      private_key:
        '-----BEGIN PRIVATE ... -----END PRIVATE KEY-----\n', (2)
      client_email:
        'langchain-vertex-ai@langchain-gemini-418916.iam.gserviceaccount.com',
      client_id: '107828751289044436034',
      auth_uri: 'https://accounts.google.com/o/oauth2/auth',
      token_uri: 'https://oauth2.googleapis.com/token',
      auth_provider_x509_cert_url: 'https://www.googleapis.com/oauth2/v1/certs',
      client_x509_cert_url:
        'https://www.googleapis.com/robot/v1/metadata/x509/langchain-vertex-ai%40langchain-gemini-418916.iam.gserviceaccount.com',
      universe_domain: 'googleapis.com',
    },
  },
};

module.exports = configuration;

npm install zod

const { z } = require('zod');
const { PromptTemplate } = require('@langchain/core/prompts');
const { StructuredOutputParser } = require('@langchain/core/output_parsers');
const { RunnableSequence } = require('@langchain/core/runnables');

class MovieRecommendationsService {
  constructor(model) {
    this.model = model; (1)

    this.parser = StructuredOutputParser.fromZodSchema( (2)
      z.object({
        movies: z
          .array(
            z.object({
              "title:" z.string().describe('title of the movie'),
              "director:" z.string().describe('director of the movie'),
              "year:" z.number().describe('year the movie was released'),
              "reason:" z
                .string()
                .describe('reason why the movie was recommended'),
            })
          )
          .describe('json array of recommended movies'),
      })
    );

    this.chain = RunnableSequence.from([ (3)
      new PromptTemplate({
        template: `Given a list of movies suggest 5 new movies. Do not repeat the movies from the list.\n{format_instructions}
        List of movies: {movies}`, (4)
        inputVariables: ['movies'], (5)
        partialVariables: {
          format_instructions: this.parser.getFormatInstructions(), (6)
        },
      }),
      this.model,
      this.parser,
    ]);
  }

  async getMovieRecommendations({ movies }) {
    const response = await this.chain.invoke({ (7)
      movies: movies.join(','),
    });

    return response;
  }
}

module.exports = MovieRecommendationsService;

const express = require('express');
const bodyParser = require('body-parser');

...

const MovieRecommendationsService = require('./services/movie-recommendations'); (1)
const configuration = require('./config/configuration'); (1)
const { VertexAI } = require('@langchain/google-vertexai'); (1)

const app = express();
app.use(bodyParser.json()); (2)

...

app.put('/post-test', async (req, res) => { (3)
  const recommendations = await new MovieRecommendationsService(
    new VertexAI({
      modelName: 'gemini-1.0-pro', (4)
      authOptions: {
        credentials: configuration.vertexAI.credentials, (5)
        projectId: configuration.vertexAI.credentials.project_id, (5)
      },
    })
  ).getMovieRecommendations(req.body); (6)
  res.send(recommendations); (7)
});

module.exports = app;

{
  "movies": [
    "The Matrix",
    "Blade Runner",
    "2001: A Space Odyssey"
  ]
}

{
  "movies": [
    {
      "title": "Eternal Sunshine of the Spotless Mind",
      "director": "Michel Gondry",
      "year": 2004,
      "reason": "A thought-provoking and emotionally resonant exploration of love, memory, and identity."
    },
    {
      "title": "Spirited Away",
      "director": "Hayao Miyazaki",
      "year": 2001,
      "reason": "A visually stunning and imaginative animated adventure that captures the wonder and challenges of childhood."
    },
    {
      "title": "The Godfather",
      "director": "Francis Ford Coppola",
      "year": 1972,
      "reason": "A gripping and epic crime saga that explores the themes of family, loyalty, and betrayal."
    },
    {
      "title": "The Shawshank Redemption",
      "director": "Frank Darabont",
      "year": 1994,
      "reason": "An uplifting and emotionally powerful story about hope, resilience, and the transformative power of friendship."
    },
    {
      "title": "Parasite",
      "director": "Bong Joon-ho",
      "year": 2019,
      "reason": "A thought-provoking and socially conscious film that explores the themes of class inequality, family dynamics, and the pursuit of wealth."
    }
  ]
}