...new Set([])

new Set实现去重

...实现解构

let set =new Set(['a','b','c','a']);

console.log(set);//Set[3]{'a','b','c'} size:3

console.log(set.size);//3

var c = [...set];

console.log(c);//['a','b','c']

console.log(c.join(','));//a,b,c

console.log(..set);这样是直接输出值的;

可是用这个

let arr = ...set;

console.log(arr);

控制台就会报错，后来发现是要在外面加个中括号 

let arr = [...set];

console.log(arr);

这样就可以了