for(let i=0 ; i<3; i++){
  let i="a";
  console.log(i); //输出三次a；在()内声明的i和在{}内声明的i并不在同一作用域内
}
console.log(i); //报错

let [a,b,c] = [1,2,3];
console.log(b); //2
 
let [d,e,f] = [1,2];
console.log(e); //2
console.log(f); //undefined；
 
let [g, [h,i]] = [1,[2,3]];
console.log(h); //2；模式匹配
 
let [j, ...k] = [1,2,3,4];
console.log(k); //[2,3,4];
let [l, ...m] = [1];
console.log(m); //[];尾部匹配

let [a="1", b] = [ ,3];
console.log(a); //1
 
let [c=d, d]=[]; //报错，因为b使用在了声明之前
let [c=d, d]=[1]; //不报错，因为没有执行c=d默认赋值

let {a , b} = {a: "aaa", b: "bbb"};
console.log(a); //"aaa"
 
let {a:b} = {a: "aaa", c: "bbb"};
console.log(b); //"aaa"
console.log(a); //error 此时a并没有被赋值，这里的a变成仅仅是匹配模式了
 
let {x=3} = {x:undefined}
console.log(x); //3
let {x=3} = {x:null}
console.log(x); //null 默认值生效的条件是赋值严格等于（===）undefined
 
let [a,b,c,d,e]="hello";
console.log(d); //"l" 字符串解构赋值，感觉挺实用
 
let {length : len}="hello";
console.log(len); //5 因为"hello"字符串对象有length属性，因此可以根据属性赋值

[a,b]=[b,a];

function f({x,y,z}){
  ...
}
f({z:3, y:2, x:1});

let data={
  id: 10,
  name: "brain1981",
  age: 35,
  skill: ["JS", "PHP"]
};
let {name, skill:skillName} = data;
console.log(name); //"brain1981"
console.log(skillName); //["JS", "PHP"]