变量解构赋值用途详解

1. 交换变量的值.

[x ,y] = [y, x];

2. 从函数返回多个值.

//数组
function example(){
  return [1, 2 , 3]
}
var [a, b, c] = example();
//对象
function example(){
  return {
      foo: 1,
      bar: 2
    }
}
var {foo, bar } = example();

3. 函数参数的定义.

//有序值
function f([x, y, z]){ ... }
f([1,2,3])
//无序值
function f({x, y, z}){ ... }
f(y: 1, z: 2, x: 3)

4. 提取json数据.

var jsonData = {
   id: 42,
   status: 'ok',
   data: [867, 5309]
}
let {id, status, data:arr} = jsonData;
console.log(id, status, arr) //  42, "ok", [867, 5309]

5. 函数的默认值.

function a(x=1, y=2){
   return  x + y ;
 };
a() / / 3

6. 遍历Map解构.

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