const robot = {
  _model: '1E78V2',
  _energyLevel: 100,
  get energyLevel() {
    if (typeof this._energyLevel === 'number') {
      return `My current energy level is ${this._energyLevel}`
    } else {
      return 'System malfunction: cannot retrieve energy level'
    }
  }
};

console.log(robot.energyLevel)