13. spread-operator

//array
const arr1 = [1, 2, 3];
const arr2 = [4, 5, 6];
const arr3 = [...arr1, ...arr2]; // [1, 2, 3, 4, 5, 6]
const arr4 = [...arr1]; // [1, 2, 3]


//object
const obj1 = { a: 1, b: 2 };
const obj2 = { c: 3, d: 4 };
const obj3 = { ...obj1, ...obj2 }; // { a: 1, b: 2, c: 3, d: 4 }
const obj4 = { ...obj1 }; // { a: 1, b: 2 }

//string
const str = "hello";
const arr = [...str]; // ["h", "e", "l", "l", "o"]