A prototype switching state machine

Account.js

import StateMachine from './StateMachine'

class Account extends StateMachine {
  constructor (initialState, initialBalance = 0) {
    super(initialState)
    this.balance = initialBalance
  }  
  
  static get openStateMethods () {
    return {
      deposit (amount) {
        return this.balance += amount
      },
      withdraw (amount) {
        return this.balance -= amount
      },
      placeHold () {
        return this.to('held')
      },
      close () {
        if (this.balance > 0) {
          // transfer balance to suspension account
        }
        return this.to('closed')
      }
    }
  }

  static get heldStateMethods () {
    return {
      removeHold () {
        return this.to('open')
      },
      deposit (amount) {
        return this.balance += amount
      },
      close () {
        if (this.balance > 0) {
          // transfer balance to suspension account
        }
        return this.to('closed')
      }
    }
  }

  static get closedStateMethods () {
    return {
      reopen () {
        // restore balance if applicable
        return this.to('open')
      }
    }
  } 
}

StateMachine.js

export default class StateMachine {
  constructor (initialState) {
    this.to(initialState)
  }

  static setStateMethods (self) {
    self.__proto__ = Object.assign({ 
      constructor: self.constructor, to: self.to
    }, self.constructor[self.state + 'StateMethods'])
  }

  static unsetStateMethods (self) {
    self.__proto__ = Object.assign({ 
      constructor: self.constructor, to: self.to
    }, self.constructor.prototype)
  }

  to (state, value) {
    this.constructor.unsetStateMethods(this)
    this.state = state
    this.constructor.setStateMethods(this)
    return value
  }
}