SOURCE

// function Ninja(level) {
//   this.skillLevel = level
// }

// const ninja = new Ninja(100)
// console.log('123')

function Ninja () {
  let skillLevel
  
  this.getSkillLevel = () => {
    return skillLevel
  }
  this.setSkillLevel = value => {
    skillLevel = value
  }
}

var ninja1 = new Ninja()
ninja1.setSkillLevel(100)
console.log(ninja1.getSkillLevel())