Calculate total number of days in a year [closed]

Question

Write javascript function that calculates total number of days for a given year.

function daysInMonth(month, year) {
  return new Date(year, month, 0).getDate();
}

var jan = daysInMonth(1, 2016);
var feb = daysInMonth(2, 2016);
var maa = daysInMonth(3, 2016);
var apr = daysInMonth(4, 2016);
var mei = daysInMonth(5, 2016);
var jul = daysInMonth(6, 2016);
var jun = daysInMonth(7, 2016);
var aug = daysInMonth(8, 2016);
var sep = daysInMonth(9, 2016);
var okt = daysInMonth(10, 2016);
var nov = daysInMonth(11, 2016);
var dec = daysInMonth(12, 2016);
var dagen = jan + feb + maa + apr + mei + jul + jun + aug + sep + okt + nov + dec;

document.write('<br> Aantal dagen van jaar 2016 zijn : ' + dagen);

but i want to change the year, to 2017 but i dont want to do that 12 times.. how can i do that in 1 time

Answer 1

You can find the number of days using the simple leap year algorithm:

In the Gregorian calendar three criteria must be taken into account to identify leap years: The year can be evenly divided by 4; If the year can be evenly divided by 100, it is NOT a leap year, unless; The year is also evenly divisible by 400. Then it is a leap year.

function daysInYear(year) {
  return ((year % 4 === 0 && year % 100 > 0) || year %400 == 0) ? 366 : 365;
}

console.log(daysInYear(2016));

console.log(daysInYear(2017));

Using loops

If it's used to teach you loops, you can use a for loop to iterate the 12 months, and calculate the total number of days:

function daysInMonth(month, year) {
  return new Date(year, month, 0).getDate();
}

function daysInYear(year) {
  var days = 0;
  
  for(var month = 1; month <= 12; month++) {
    days += daysInMonth(month, year);
  }
  
  return days;
}

console.log('2016: ', daysInYear(2016));
console.log('2017: ', daysInYear(2017));