In ES5, the assignment of various variables and objects can only be one-to-one. es6 has been reformed. The new standard allows us to assign in groups. Variables correspond to the position of values and assign one by one. This is deconstruction assignment.

let [w,b,i]='wbi';
console.log(w,b,i);//w b i

let [w,b]='wbiokr';
console.log(w,b);//w,b

let [w,b,i,o]='wb';
console.log(w,b,i,o);//w,b,undefined,undefined

let [(w)]='wbiokr';//Parentheses, report the error at this time! ___________

[(w)]='wbiokr';
console.log(w);//w In the current case, parentheses do not report errors

let [a,b,c]=[1,2,3];
console.log(a,b,c);//1,2,3

let [a,b]=[1,2,3,4];
console.log(a,b);//1,2

let [,a,b]=[1,2,3,4];
console.log(a,b);//2,3

let [a,b,c]=[1];
console.log(a,b,c);//1,undefined,undefined

let [a,b,c]=[1,2,[3]];
console.log(a,b,c);//1,2,[3]

let [a,[b]]=[1,2];//Report errors!!!!!!!!!

let [a,[b]]=[1,[2]];
console.log(a,b);//1,2

let [a,b]={a:1,b:2}//Report errors!!!!!!!!!!

let [(a)]=[1];//Wrong report, bracket question!!!

[(a)]=[1];
console.log(a);//1. In the current case, parentheses do not report errors

let {a}={a:1};
console.log(a);//1

let {b}={a:1};
console.log(b);//undefined

let {a:c}={a:1};
console.log(c);//1

let a;
let {a}={a:1};//Error reporting, when associated with let's characteristics, can not be redefined

let a;
{a}={a:1};
console.log(a);//No error was reported. Result: 1

let c;
let {a:c}={a:1};//Reporting errors, the same

let c;
{a:c}={a:1};
console.log(c);//1

let {a,b:{c}}={a:1,b:{c:3}};
console.log(a,b,c);//1,undefined,3

let {(aaaaq)}={aaaaq:1};//Error reporting, parentheses

let {a:(a)}={a:1};//Error reporting, parentheses

{a:(a)}={a:1};
console.log(a);//1 In the current case, parentheses do not report errors

(function([a,b,c]){console.log(a,b,c)})([1,2,3]);//1,2,3

[[1,2],[3,4]].reduce(function([a,b]){console.log(a*b)});//2 , 12

let [a=1]=[];
console.log(a);//1

let {a,b=true}={a:2};
console.log(a,b);//2,true

let {a=true}={a:NaN};
console.log(a);//NaN

let {a=true}={a:null};
console.log(a);//null;

let {a=true}={a:undefined};
console.log(a);//true

function fun(x=1,y=2){
    console.log(x,y)
};
fun('s');//'s 2
fun(2,5);//2,5
fun();//1,2 defaults to 1,2

function fun2({x,y}={x:1,y:2}){
    console.log(x,y);
}//The default parameter value of fun2 function is to earn a parameter object
fun2();//1,2 also outputs default values
fun2({x:2});//2 undefined

———-

//Define X=2, Y=5 and exchange X, Y without the help of the third value. The result should be x=5,y=2.

var x=2,y=5;
x=y-x;//At this point x=3,y=5
y=y-x;//At this point x=3,y=2
x=y+x;//At this point x=5,y=2

///////If hard es6 What about structural assignment?.......
let x=2,y=5;
[x,y]=[y,x];
console.log(x,y)//5,2 Perfect!!!!!!!