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去重

//定义常量 res,值为一个Map对象实例
//返回arr数组过滤后的结果，结果为一个数组
//过滤条件是，如果res中没有某个键，就设置这个键的值为
const res = new Map();
const arr = [1,1,2,2,3,4,4,5,6,6,6,6,4,3];
const result = arr.filter((a) => !res.has(a) && res.set(a, 1));
console.log(result); //[1,2,3,4,5,6]

并集

let a = [1, 2, 3];
let b = [2, 4, 5];
let union = a.concat(b.filter(v => !a.includes(v)));
console.log(union) // [1,2,3,4,5]

交集

let a = [1, 2, 3];
let b = [2, 4, 5];
let intersection = a.filter(v => b.includes(v));
console.log(intersection); // [2]

差集

let a = [1, 2, 3];
let b = [2, 4, 5];
let difference = a.concat(b)
                  .filter(v => !a.includes(v) || !b.includes(v));

console.log(difference)// [1,3,4,5]