数组去重

// 第一种方法
let arr = [1,1,2,3,4];
function fun(v) {
    return Array.from(new Set(v))
}
console.log(fun(arr)) //[1,2,3,4]
// 第二种方法
let qc= [...new Set(arr)]

console.log(qc) //[1,2,3,4]

数组并集

let arr0 = ['a','b','c'];
let arr2 = ['c','d'];
let a=new Set(arr0);
let b=new Set(arr2);
let bj = new Set([...a,...b]);

console.log(bj);//{“a”, “b”, “c”, “d”}

数组交集

let jj = new Set([…a].filter(x=>b.includes(x)));
console.log(jj);//{“c”}

数组差集

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

console.log(cj);//{“a”, “b”}

统计数组相同项的个数

let arr6=['a','a','a','b','c','c'];
let arr6obj=arr6.reduce(function(obj,name){
    obj[name]=obj[name]?++obj[name]:1;
    return obj;
},{})

console.log(arr6obj)// {a: 3, b: 1, c: 2}

数组方法reduce()实现filter、map

let arr7=[2,3,10];
const arro=arr7.reduce(function(list,num){
    num=num*2;
    if(num>=20){
        list.push(num)
    }
    return list;
},[])

console.log(arro);//[20]

字符串转换为数字

let num1='1' * 1;

console.log(typeof num1) //number

使用Boolean过滤数组中的所有假值

let jz=[0,null,false,NaN,1,2];
const filter1=arr1=>arr1.filter(Boolean);

console.log(filter1(jz)) //[1,2]

取整

let num2=1.223;

console.log(num2|0);//1

判断奇偶

let num3=3;

console.log(!!(num3 & 1));//true

更多请见：http://www.mark-to-win.com/tutorial/50933.html