PromptContainer.js

import React from 'react'
import Prompt from '../components/Prompt'

class PromptContainer extends React.Component {
  constructor(props) {
    super(props)
    this.state = { username: '' }
    this.handleUpdateUser = this.handleUpdateUser.bind(this);
    this.handleSubmitUser = this.handleSubmitUser.bind(this);
  }
  
  // ...
}