action.js

//@flow
import {rootDomain} from 'effector'
import type {OrderedSet} from 'immutable'

const domain = rootDomain.domain('user list')

type User = {
  username: string
}

export const user: OrderedSet<User> = domain.OrderedSet()

AddUser.js

//@flow

import {user} from './action'

class AddUser extends React.Component<{
  addUser: typeof user.add
}, {username: string}> {
  render() {
    const {username, addUser} = this.props
    return (
      <form>
        <input value={username} />
        <button onClick={() => this.addUser({username})}>Submit</button>
      </form>
    )
  }
}

export default connect(null, {addUser: user.add})(AddUser)

reducer.js

import {user} from './action'

const reducer = user
  .reducer
  .reset(logoutUser)