[JS] 최신문법 (ES6, ES11)

ES6

Shorthand property names

/**
 * Shorthand property names
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Object_initializer
 *
 */

{
  const ellie1 = {
    name: 'Ellie',
    age: '18',
  };

  const name = 'Ellie';
  const age = '18';

  // 💩
  const ellie2 = {
    name: name, //Ellie
    age: age, //18
  };

  // ✨ 축약해서 코드 작성 가능
  const ellie3 = {  
    name,
    age,
  };

  console.log(ellie1, ellie2, ellie3);
  console.clear();
}

 

Destructuring Assignment

/**
 * Destructuring Assignment
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Destructuring_assignment
 *
 */
{
  // object
  const student = {
    name: 'Anna',
    level: 1,
  };

  // 💩
  {
    const name = student.name;
    const level = student.level;
    console.log(name, level);
  }

  // ✨
  {
    const { name, level } = student; 
    console.log(name, level); //Anna 1

    //키의 이름을 변경할 수도 있음
    const { name: studentName, level: studentLevel } = student;
    console.log(studentName, studentLevel); //Anna 1
  }

  // array
  const animals = ['🐶', '😽'];

  // 💩
  {
    const first = animals[0];
    const second = animals[1];
    console.log(first, second);
  }

  // ✨
  {
    const [first, second] = animals; //0, 1번째에 접근 ( 강아지 고양이)
    console.log(first, second);
  }
  console.clear();
}

 

Spread Syntax

/**
 * Spread Syntax
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Spread_syntax
 *
 */
{
  const obj1 = { key: 'key1' };
  const obj2 = { key: 'key2' };
  const array = [obj1, obj2];

  // array copy
  const arrayCopy = [...array]; //🌟object의 참조값을 복사 받음
  console.log(array, arrayCopy);

  const arrayCopy2 = [...array, { key: 'key3' }];
  obj1.key = 'newKey'; //🌟따라서 값을 바꾸면 전체가 다 바뀜(참조값을 복사 받아서)
  console.log(array, arrayCopy, arrayCopy2);


  // object copy
  const obj3 = { ...obj1 };
  console.log(obj3);

  // array concatenation
  const fruits1 = ['🍑', '🍓'];
  const fruits2 = ['🍌', '🥝'];
  const fruits = [...fruits1, ...fruits2];
  console.log(fruits); //복숭,딸기,바나나,키위

  // object merge
  const dog1 = { dog: '🐕' };
  const dog2 = { dog: '🐶' };
  const dog = { ...dog1, ...dog2 };
  console.log(dog); //🚨만약 키가 값은 object를 병합하면 뒤에꺼가 앞에꺼를 덮어씀
  console.clear();
}

 

Default parameters

/**
 * Default parameters
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Functions/Default_parameters
 */
{
  // 💩
  {
    function printMessage(message) {
      if (message == null) {
        message = 'default message';
      }
      console.log(message);
    }

    printMessage('hello');
    printMessage(); //undefined
  }

  // ✨
  {
    function printMessage(message = 'default message') { //초기값을 지정
      console.log(message); 
    }

    printMessage('hello');
    printMessage();
  }
  console.clear();
}

 

Ternary Operator

/**
 * Ternary Operator
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Conditional_Operator
 */
{
  const isCat = true;
  // 💩
  {
    let component;
    if (isCat) {
      component = '😸';
    } else {
      component = '🐶';
    }
    console.log(component);
  }

  // ✨
  {
    const component = isCat ? '😸' : '🐶';
    console.log(component);
    console.log(isCat ? '😸' : '🐶');
  }
  console.clear();
}

 

Template Literals

/**
 * Template Literals
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Template_literals
 */
{
  const weather = '🌤';
  const temparature = '16°C';

  // 💩
  console.log(
    'Today weather is ' + weather + ' and temparature is ' + temparature + '.'
  );

  // ✨
  console.log(`Today weather is ${weather} and temparature is ${temparature}.`);

}

 

---

ES11

Optional Chaining

/**
 * Optional Chaining (ES11)
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Optional_chaining
 */
{
  const person1 = {
    name: 'Ellie',
    job: {
      title: 'S/W Engineer',
      manager: {
        name: 'Bob',
      },
    },
  };

  const person2 = {
    name: 'Bob',
  };

  // 💩💩💩💩💩💩
  {
    function printManager(person) {
      console.log(person.job.manager.name);
    }
    printManager(person1);
    // printManager(person2);
  }

  // 💩💩💩 Ternary Operator 사용
  {
    function printManager(person) {
      console.log(
        person.job
          ? person.job.manager
            ? person.job.manager.name
            : undefined
          : undefined
      );
    }
    printManager(person1);
    printManager(person2);
  }

  // 💩
  {
    function printManager(person) {
      console.log(person.job && person.job.manager && person.job.manager.name);
    }
    printManager(person1);
    printManager(person2);
  }

  // ✨
  {
    function printManager(person) {
      console.log(person.job?.manager?.name);
    }
    printManager(person1);
    printManager(person2);
  }
  console.clear();
}

 

 

Nullish Coalescing Operator

/**
 * Nullish Coalescing Operator (ES11)
 * https://developer.mozilla.org/ko/docs/Web/JavaScript/Reference/Operators/Nullish_coalescing_operator
 */
{
  // Logical OR operator
  // false: false, '', 0, null, undefined
  {
    const name = 'Ellie';
    const userName = name || 'Guest';
    console.log(userName);
  }

  {
    const name = null;
    const userName = name || 'Guest'; 
    console.log(userName);
  }

  // 💩
  {
    const name = '';
    const userName = name || 'Guest'; //''도 false로 간주되서 Guest가 할당..이름을 안쓰고 싶은데..
    console.log(userName); //Guest

    const num = 0;
    const message = num || 'undefined'; //undefined로 할당
    console.log(message); //undefined
  }

  // ✨
  {
    const name = '';
    const userName = name ?? 'Guest'; //이름이 있다면 name을 쓰고, 값이 없다면 Guest
    console.log(userName);  //   출력

    const num = 0;
    const message = num ?? 'undefined'; //num이 있다면 num쓰고, 없으면 undefined
    console.log(message); //0
  }
}