gistfile1.js

var Sequelize = require('sequelize'),
    DataTypes = Sequelize,
    sequelize = new Sequelize('groups_test', 'root', 'password');

var Device = sequelize.define('Device', {
  name: DataTypes.STRING
}, {
  underscored: true,
  timestamps: false
});

var Group = sequelize.define('Group', {
  name: DataTypes.STRING
}, {
  underscored: true,
  timestamps: false
});

Group.belongsToMany(Device);
Device.belongsToMany(Group);

sequelize.sync({force: true})
  .then(function() {
    return Promise.all([
      Device.create({ name: 'device1' }),
      Device.create({ name: 'device2' }),
      Group.create({ name: 'group1' }),
      Group.create({ name: 'group2' }),
      Group.create({ name: 'group3' })
    ]);
  })
  .spread(function(device1, device2, group1, group2, group3) {
    return Promise.all([
      device1.setGroups([group1, group2, group3]),
      device2.setGroups([group3])
    ]);
  })
  .then(function() {
    return Device.find({
      include: [
        { model: Group, where: { name: 'group2' } }
      ]
    });
  })
  .then(function(devices) {
    console.log(devices);
  });