Using Sequelize with Webpack can be interesting. This snippet should help...

index.js

import Sequelize from 'sequelize';
import config from '../config';

// Face, meet desk. Sequelize models and Webpack do not play nicely
let models = {};

(function(config) {
  if (Object.keys(models).length && !force) {
    return models;
  }

  const sequelize = new Sequelize(config.byteTestDb, config.byteTestUser, config.byteTestPwd, { dialect: 'mssql', logging: false, host: config.byteTestDbHost, define: { timestamps: false }});

  // Importing each module for now, can change to readDirSync and require models dynamically
  let modules = [
    require('./FileData.js'),
  ];

  modules.forEach((module) => {
    const model = module(sequelize, Sequelize, config);
    models[model.name] = model;
  });

  Object.keys(models).forEach((key) => {
    if ('associate' in models[key]) {
      models[key].associate(models);
    }
  });

  models.sequelize = sequelize;
  models.Sequelize = Sequelize;

  return models;
})(config);

module.exports = models;

A similar solution to this gist was posted in this issue. sequelize/sequelize#4974

SOLVED - This worked for me. If you want to make webpack config for all sequelize models dynamically check this out. - webpack/webpack#4879