一些js小知识

一、数组去重

ES6写法：
1、set 、Array.from

var arr = [1,2,22,22,3,4,5,5,6]
var set = new Set(arr)     //{1,2,3,4,6}
var setArr = Array.from(set)  //讲set结构转为数组array
console.log(setArr)   //[1,2,3,4,6]

2、...(拓展运算符) + set

var arr = [1,1,2,3,4]
var tt = [...new Set(arr)]
console.log(tt)   //[1,2,3,4]

ES5写法：

var arr = [1,2,3,3,4,4,4,5]
var temObj = {}
var result = []
arr.forEach(function(a){
  var key = (typeof a) + a;
  if(!temObj[key]){
    temObj[key] = true;
    result.push(a)
  }
})
console.log(result)

二、时间戳转换为日期

var t = 1521694261;
timestampToTime(t);

function timestampToTime(timestamp){
  var date = new Date(timestamp * 1000);    //时间戳为10位需*1000，时间戳为13位的话不需乘1000
  year = date.getFullyear();
  month = date.getMonth() + 1 < 10 ? "0" + (date.getMonth() + 1) : date.getMonth() + 1;
  day = change(date.getDate());
  hour = change(date.getHours());
  minute = change(date.getMinutes());
  second = change(date.getSeconds());
  var times = year + '-' + month + '-' + day + ' ' + hour + ':' + minute + ':' + second;
   console.log(times)
}
function change(t){
  if(t < 10){
      return "0" + t
  }else{
    return t
  }
}

三、js千位分割符

var separator = (num) => {
  if(!num){
      return '0.00';
  }
 let str = parseFloat(num).toFixed(2);
 return str && str
    .toString()
    .replace(/(d)(?=(d{3})+.)/g, function($0, $1) {
    return $1 + ",";
 })
}

separator(386485473.88) //"386,485,473.88"