postgres init code with multiple sequelize

I am trying to convert js code to ts code (and understanding why something have been done).

This my JS code

use strict';

const fs = require('fs');
const path = require('path');
const Sequelize = require('sequelize');
const basename = path.basename(__filename);
const env = process.env.NODE_ENV || 'development';
const config = require(__dirname + '/../config/config.js')[env];
const db = {};

let sequelize;
if (config.use_env_variable) {
  sequelize = new Sequelize(process.env[config.use_env_variable], config);
} else {
  sequelize = new Sequelize(config.database, config.username, config.password, config);
}


Object.keys(db).forEach(modelName => {
  if (db[modelName].associate) {
    db[modelName].associate(db);
  }
});

db.sequelize = sequelize;
db.Sequelize = Sequelize;

module.exports = db;

Here, there are multiple sequalise

db.sequelize = sequelize;
db.Sequelize = Sequelize;

Can someone please help me in understand meaning, purpose and why both of them exist? and where we would use each of them.

I am able to make sense for sequelize but not for Sequelize. like we already have used new Sequelize( so why would we add it in db object?

from postgres init code with multiple sequelize