JS deconstruction assignment

1. Deconstruction and assignment of arrays

//  For unwanted values , Use ',', Skip the value .
const [first, , third, ...rest] = [1, 2, 3, 4, 5];
console.log(first) // 1
console.log(third) // 3
console.log(rest)  // [4, 5]

const [a, b = 'default'] = []
console.log(a,b) // undefined 'default'

String、Set、Map All traversable objects can adopt deconstruction assignment ：

// String
const [A,B,C,D] = 'abcd'
console.log(A,B,C,D) // a b c d

// Set
const[one, two, three, four] = new Set([1, 2, 3, 4])
console.log(one,two,three,four) // a b c d

2. Object's deconstruction assignment

let info = {
    
  name:"David",
  age: 24,
  weight: 180
};
// 1. Also use '=' Give default values  2. The variable name can be given a new name by deconstruction 
let {
     name, age = 18, weight:height } = info;
console.log(name, age, height) // David 24 180

// 2. Take only some variables 
let {
     name: nickname, ...rest } = info;
console.log(nickname, rest) // David {age: 24, weight: 180}

// 3. More nesting levels , It can be correctly deconstructed only by corresponding to the order and level 
let cellPhone = {
    
	size: {
    
		width: 375,
		height: 667
	},
	package: ['type1', 'type2'],
	price: 8888,
};

let {
     size: {
    width, height: weight }, package: [, t2 ], price } = cellPhone;
console.log(weight, t2) // 667 "type2"

Change the attribute value of the object by deconstructing the assignment

const obj = {
    a: '123', b: '456'};
[obj.a, obj.b] = ['aaa', 'bbb'];
console.log(obj); // {a: "aaa", b: "bbb"}

stay for…of Use in

const obj = {
    a: '123', b: '456'};
for (let [k, v] of Object.entries(obj)) {
    
	console.log(k, v)
}

// a '123'
// b '456'