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

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

 let [d,,e] = [1,2,3];
 console.log(e); //3

 let [f,...tail] = [1,2,3];
 console.log(tail); //[2, 3]

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

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

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

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

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

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

function f(){
  alert(1);
 }
 let [a = f()] = [3]; //f()不会执行
 let [b = f()] = [undefined]; //会执行

 let {foo,bar} = {foo:1,bar:2};
 console.log(foo); //1

 let {bar,foo} = {foo:1,bar:2};
 console.log(foo);//1

 let {first: f,last: l} = {first:1,last:3};
 console.log(l); //3

let obj = {
  a:1,
  b:[
   'hello',
   {c:'world'}
  ]
 }
 let {a: a,b: [h,{c:w}]} = obj;
 console.log(a); //1
 console.log(h); //hello
 console.log(w); //world

 let {x: x = 1,y: y=2,z: z=3,w: w} = {x:3,y:null,z:undefined};
 console.log(x) //3
 console.log(y) //null
 console.log(z) //3
 console.log(w) //undefined 

 let [a,b,c] = 'hello';
 console.log(a); //h
 console.log(b); //e
 console.log(c); //l

let {toString: s} = 123;
s === Number.prototype.toString // true

let {toString: a} = true;
a === Boolean.prototype.toString // true