スプレッド＆レスト演算子

const nums = [5,6,7];
const newNums = [1,2, nums[0],nums[1],nums[2]];
console.log(newNums); // [ 1, 2, 5, 6, 7 ]

is reduced to 

const nums = [5,6,7];
const newNums = [1,2, ...nums];
console.log(newNums); // [ 1, 2, 5, 6, 7 ]
console.log(...newNums); // 1 2 5 6 7

const arr1 = [1,2,3,4,5];
const arr2 = [6,7,8,9];

let nums = [...arr1,...arr2];
nums; // [ 1, 2, 3, 4, 5, 6, 7, 8, 9 ]


const firstname = "Peter";
const fullName = [...firstname,' ',"P."];
fullName; // [ 'P', 'e', 't', 'e', 'r', ' ', 'P.' ]

console.log(...firstname); // 'P' 'e' 't' 'e' 'r'

const girl = {
  name: 'Melania',
  friends: ['Alina', 'Alice', 'Ayesha', 'Anamika', 'Anaya']
};

const frnz = [...girl.friends];
console.log(frnz); // [ 'Alina', 'Alice', 'Ayesha', 'Anamika', 'Anaya' ]
console.log(girl.friends); // [ 'Alina', 'Alice', 'Ayesha', 'Anamika', 'Anaya' ]

let male = {
  "firstName": "Gangadhar",
  "lastName": "Shaktimaan"
}

let female = {
  "firstName": "Geeta",
  "lastName": "Vishwas"
}

let x = {...male, born: 1950};
let y = {...female, born: 1940};

x; // { firstName: 'Gangadhar',   lastName: 'Shaktimaan',   born: 1950 }
y; // { firstName: 'Geeta',  lastName: 'Vishwas',  born: 1940 }```




## Shallow Copy of objects:

let male = {
  "firstName": "Gangadhar",
  "lastName": "Shaktimaan"
}

let character = {...male, firstName: 'Wonderwoman'};

male;         // { firstName: 'Gangadhar', lastName: 'Shaktimaan' }
character;    // { firstName: 'Wonderwoman', lastName: 'Shaktimaan' }

- First name for character object is changed although it was extracted from male object

## Rest syntax collects all the elements after the last elements into an array. Doesn't include any skipped elements. 
- Hence, it should be the last element in the destructuring assignment.
- There can be only one rest in any destructuring assignment.

- Rest also works with objects. Only difference is that elements will be collected into a new object instead of an arrray.

- Although both look same, but they work differently based on where they are used.