# 디스트럭처링

let  x,  y,  z;  
[x,  y]  =  [1,  2];  
console.log(x,  y);  // 1 2  
[x,  y]  =  [1];  
console.log(x,  y);  // 1 undefined  
[x,  y]  =  [1,  2,  3];  
console.log(x,  y);  // 1 2  
[x,  ,  z]  =  [1,  2,  3];  
console.log(x,  z);  // 1 3  
// 기본값  
[x,  y,  z  =  3]  =  [1,  2];  
console.log(x,  y,  z);  // 1 2 3  
[x,  y  =  10,  z  =  3]  =  [1,  2];  
console.log(x,  y,  z);  // 1 2 3  
// spread 연산자  
[x,  ...y]  =  [1,  2,  3];  
console.log(x,  y);  // 1 [ 2, 3 ]

const  today  =  new  Date();  
const  formattedDate  =  today.toISOString().substring(0,  10);  
const  [year,  month,  day]  =  formattedDate.split('-');  
console.log([year,  month,  day]);  // [ '2018', '05', '05' ]

// ES6 Destructuring  
const  obj  =  {  firstName:  'Ungmo',  lastName:  'Lee'  };  
const  {  firstName,  lastName  }  =  obj;  
console.log(firstName,  lastName);  // Ungmo Lee

const  todos  =  [  
	{  id:  1,  content:  'HTML',  completed:  true  },  
	{  id:  2,  content:  'CSS',  completed:  false  },  
	{  id:  3,  content:  'JS',  completed:  false  }  
];  
// todos 배열의 요소인 객체로부터 completed 프로퍼티만을 추출한다.  
const  completedTodos  =  todos.filter(({  completed  })  =>  completed);  
console.log(completedTodos);  // [ { id: 1, content: 'HTML', completed: true } ]

const  person  =  {  
	name:  'Lee',  
	address:  {  
		zipCode:  '03068',  
		city:  'Seoul'  
	}  
};  
const  {  address:  {  city  }  }  =  person;  
console.log(city);  // 'Seoul'