es6的一些笔记（交集，并集，差集）

let a = new Set ( [ 1 , 2 , 3 ] ) ;

let b = new Set ( [ 4 , 3 , 2 ] ) ;

// 并集

let union = new Set ( [ . . . a , . . . b ] ) ;

// Set {1, 2, 3, 4}

// 交集

let intersect = new Set ( [ . . . a ] . filter ( x = > b . has ( x ) ) ) ;

// set {2, 3}

// 差集

let difference = new Set ( [ . . . a ] . filter ( x = > ! b . has ( x ) ) ) ;

// Set {1}