Overview
 Destructuring assignment is an extension of the assignment operator.

It is a kind of pattern matching against arrays or objects, and then assigning values ​​to the variables.

The code is concise and easy to read, and the semantics are clearer; it also facilitates the acquisition of data fields in complex objects.

Deconstructing the model
 In deconstruction, the following two parts are involved:

The source of destructuring, the right part of the destructuring assignment expression.
The target of destructuring, the left part of the destructuring assignment expression.
Destructuring of an array model ( Array)
basic

let [a, b, c] = [1, 2, 3];
// a = 1
// b = 2
// c = 3
 Nestable

let [a, [[b], c]] = [1, [[2], 3]];
// a = 1
// b = 2
// c = 3
 Ignorable

let [a, , b] = [1, 2, 3];
// a = 1
// b = 3
 incomplete deconstruction

let [a = 1, b] = []; // a = 1, b = undefined
 remainder operator

let [a, ...b] = [1, 2, 3];
//a = 1
//b = [2, 3]
string etc.

In the destructuring of the array, if the target of the destructuring is a traversable object, the destructuring assignment can be performed. Traversable objects are implemented Iterator interface data.

let [a, b, c, d, e] = 'hello';
// a = 'h'
// b = 'e'
// c = 'l'
// d = 'l'
// e = 'o'
Destructuring default values

let [a = 2] = [undefined]; // a = 2
 When the destructuring pattern has a matching result, and the matching result is undefined When the default value is triggered as the return result.

let [a = 3, b = a] = [];     // a = 3, b = 3
let [a = 3, b = a] = [1];    // a = 1, b = 1
let [a = 3, b = a] = [1, 2]; // a = 1, b = 2
a and b The matching result is undefined ，Trigger defaults: a = 3; b = a =3
a Normal destructuring assignment, matching results: a = 1，b match result undefined ，Trigger defaults: b = a =1
a and b Normal destructuring assignment, matching results: a = 1，b = 2
 Deconstruction of the object model ( Object)
basic

let { foo, bar } = { foo: 'aaa', bar: 'bbb' };
// foo = 'aaa'
// bar = 'bbb'
 
let { baz : foo } = { baz : 'ddd' };
// foo = 'ddd'
Can be nested or ignored

let obj = {p: ['hello', {y: 'world'}] };
let {p: [x, { y }] } = obj;
// x = 'hello'
// y = 'world'
let obj = {p: ['hello', {y: 'world'}] };
let {p: [x, {  }] } = obj;
// x = 'hello'
incomplete deconstruction

let obj = {p: [{y: 'world'}] };
let {p: [{ y }, x ] } = obj;
// x = undefined
// y = 'world'
remainder operator

let {a, b, ...rest} = {a: 10, b: 20, c: 30, d: 40};
// a = 10
// b = 20
// rest = {c: 30, d: 40}
Destructuring default values

let {a = 10, b = 5} = {a: 3};
// a = 3; b = 5;
let {a: aa = 10, b: bb = 5} = {a: 3};
// aa = 3; bb = 5;