Default parameters, Rest parameters

// Default parameters (added in ES6)
function showMessage(message, from = 'unknown') {
  console.log(`${message} by ${from}`); // Hi! by unknown
}
showMessage('Hi!');

from의 default value 설정

// Rest parameters (added in ES6)
function printAll(...args) {
  for (let i = 0; i < args.length; i++) {
    console.log(args[i]);
  }

  for (const arg of args) {
    console.log(arg);
  }

  args.forEach((arg) => console.log(arg));
}
printAll('dream', 'coding', 'ellie');

(...args) 배열 형태 매개변수

출처: https://www.youtube.com/watch?v=e_lU39U-5bQ&feature=youtu.be