StatePattern.js

// Le Context
class TrafficLight {
  constructor() {
    this._states = [
      new GreenLight(),
      new YellowLight(),
      new RedLight()
    ]
    this._currentLight = this._states[0]
  }
  
  handleTraffic() {
    const totalStates = this._states.length
    const currentIndex = this._states.findIndex(light => light === this._currentLight)
    
    if (currentIndex + 1 < totalStates) {
      this._currentLight = this._states[currentIndex + 1]
    } else {
      this._currentLight = this._states[0]
    }
  }
  
  sign() {
    return this._currentLight.sign()
  }
}

// Les States
class RedLight {
  constructor() {
    this._light = 'red'
  }
  
  sign() {
    return "S'arreter"
  }
}

class YellowLight {
  constructor() {
    this._light = 'yellow'
  }
  
  sign() {
    return 'Ralentir'
  }
}

class GreenLight {
  constructor() {
    this._light = 'green'
  }
  
  sign() {
    return 'Démarrer'
  }
}


const Context = new TrafficLight()

console.log(Context.sign())
Context.handleTraffic()

console.log(Context.sign())
Context.handleTraffic()

console.log(Context.sign())
Context.handleTraffic()

console.log(Context.sign())
Context.handleTraffic()