ES6新特性四：变量的解构赋值实例

//① 可以从数组中提取值，按照对应位置，对变量赋值
var [a, b] = [1, 2]; //a = 1;b = 2
//② 下面是一些使用嵌套数组进行解构
var [d, [[c], f]] = [1, [[2], 3]];
var [,,third] = ["foo", "bar", "baz"];//third = "baz"
var [head, ...tail] = [1, 2, 3, 4];//head = 1;tail = [2, 3, 4]
//③不完全结构
var [x, y] = [1,2,6]; //x = 1;y = 2
//④ 解构赋值允许指定默认值
var [foo = true] = []; //foo = true
var [x, y='b'] = ['a'] // x='a', y='b'
var [x, y='b'] = ['a', undefined] // x='a', y='b'
//⑤ 解构不成功，变量的值就等于undefined
var [a6, a7] = [1]; //a7 = undefined

[a, b, c] = new Set(["a", "b", "c"])
console.log(a) // "a"

//对象的属性没有次序，变量必须与属性同名，才能取到正确的值
var { x, y } = { x: "aaa", y: "bbb" };//x = aaa, y = bbbb
var { c } = { a: "aaa", b: "bbb" }; // c = undefined
//严格遵守变量名与属性同名
var { d: e } = { d: "aaa", f: "bbb" }; //e = aaa
//指定默认值
var {x, y = 5} = {x: 1};// x = 1,y = 5

var map = new Map();
map.set('first', 'hello');
map.set('second', 'world');
//获取键值对
for (let [key,value] of map) {
  console.log(key + " is " + value);
}
// 获取键名
for (let [key] of map) {
  console.log(key);
}
// 获取值
for (let [,value] of map) {
  console.log(value);
}