javascript 常用方法(Date)

1 某天前后几天日期

function addDayToDate(date, num) {
  //num 为正数表示num天后，负数表示num天前  
  const d = new Date(date); 
  const day = d.getDate(); 
  d.setDate(day + num); 
  return d.toISOString().split("T")[0];
}

 2 某天是当年的第几天

function daysOfYear(dateStr) {  
    const d = new Date(dateStr);  
    const date = new Date(d.getFullYear(), 0, 0); 
    const num = Math.floor((d - date) / 1000 / 3600 / 24); 
    return num;
}

3 获取当前时间 年月日时分秒星期

/** * * @param {number|string|object} time * @param {string} cFormat */

function formatTime(time, cFormat) {

  // 不传默认今天  
  let date = time;  
  const dayStr = ["日", "一", "二", "三", "四", "五", "六"];  
  const format = cFormat || "y-m-d h:i:s";
  if (!time) {    
      date = new Date();  
   }
  if (typeof date == "string") { 
   //  2020-12-24    
      date = date.replace(/-/gm, "/");    
      date = new Date(date);  
   }
  const formatObj = {    
     y: date.getFullYear(),    
     m: date.getMonth() + 1,    
     d: date.getDate(),    
     h: date.getHours(),    
     i: date.getMinutes(),   
     s: date.getSeconds(), 
     a: date.getDay()  
  };
  const timeStr = format.replace(/([ymdhisa])+/g, (result, key) => {    
        let value = formatObj[key];    
        if (key == "a") {      
            return "星期" + dayStr[value];    
         }   
        return value.toString().padStart(2, "0");  
   });  
   return timeStr;

}