객체에 속성이 있는지 확인(freecodecamp 노트)

let users = {
  Alan: {
    age: 27,
    online: true
  },
  Jeff: {
    age: 32,
    online: true
  },
  Sarah: {
    age: 48,
    online: true
  },
  Ryan: {
    age: 19,
    online: true
  }
};

function isEveryoneHere(userObj) {
  // Only change code below this line

  // Only change code above this line
}

function isEveryoneHere(userObj) {
  // Only change code below this line
  if (userObj.hasOwnProperty('Alan') && 
      userObj.hasOwnProperty('Jeff') && 
      userObj.hasOwnProperty('Sarah') && 
       userObj.hasOwnProperty('Ryan'))
   {

       return true
    }
  else {
    return false
  }
  // Only change code above this line
}