Nodejs Year Calculate yearStartDay()

Method Source Code

Date.prototype.yearStartDay = function(){
   return new Date(this.getFullYear(),0,1).getDay();
}

Related

1. isThisYear()

   Date.prototype.isThisYear = function() {
       return new Date().getYear() == this.getYear();
   };
   

2. subYears(value)

   Date.prototype.subYears = function(value) {
     var month = this.getMonth();
     this.setFullYear(this.getFullYear() - value);
     if (month < this.getMonth()) {
       this.setDate(0);
     return this;
   };
   

3. toYearEnd()

   Date.prototype.toYearEnd = function () {
       var date = new Date(this);
       date.setMonth(12);
       date.setDate(0);
       return date;
   };
   

4. toYearStart()

   Date.prototype.toYearStart = function () {
       var date = new Date(this);
       date.setMonth(0);
       date.setDate(1);
       return date;
   };
   

5. weekOfYear()

   Date.prototype.weekOfYear = function () {
       var year = this.getFullYear();
       var d = new Date(this);
       d.setHours(0, 0, 0, 0);
       var yearStart = new Date(year, 0, 1);
       d.setDate(d.getDate() + yearStart.getDay());
       var deltaDay = (d.getTime() - yearStart.getTime()) / 86400000 + 1;
       var weekNo = Math.ceil(deltaDay / 7);
       return [year, weekNo];
   ...