Styjun

I have a function in Javascript that returns the date ranges of the current/previous/next quarter. For example, for current quarter it would return 2019-01-01 and 2019-03-31. For some reason, a few colleagues have said that the date ranges are inaccurate for them: for them it returns 2018-12-31 and 2019-02-27. I noticed that both of these users are in Germany/Poland region.

Here is my jsFiddle

function formatDate(date) 
 var d = new Date(date),
 month = '' + (d.getUTCMonth() + 1),
 day = '' + d.getUTCDate(),
 year = d.getUTCFullYear();

 if (month.length < 2) month = '0' + month;
 if (day.length < 2) day = '0' + day;

 return [year, month, day].join('-');


function getDate_FQ(range)
 var now = new Date();
 switch(range)
 case 'Previous FQ':
 now.setMonth(now.getMonth()-3);
 break;
 case 'Next FQ':
 now.setMonth(now.getMonth()+3);
 break;
 case 'Current FQ':
 break;
 
 var quarter = Math.floor((now.getUTCMonth() / 3));
 var firstDate = new Date(now.getUTCFullYear(), quarter * 3, 1);
 var endDate = new Date(firstDate.getUTCFullYear(), firstDate.getUTCMonth() + 3, 0);
 return([firstDate, endDate])


let [first, end] = getDate_FQ('Current FQ')
console.log(formatDate(first), formatDate(end))

How is it that one date is off by 1 day and the other is off by 1 month and 1 day?

If you want to have Date refers to the same time in every timezone, work in UTC and change your code in two lines to:

var firstDate = new Date(Date.UTC(now.getUTCFullYear(), quarter * 3, 1));
var endDate = new Date(Date.UTC(firstDate.getUTCFullYear(), firstDate.getUTCMonth() + 3, 0));

NaDeR Star posted a solution that solved my problem with the timezone but I found a method that was nearly twice as fast when running this 100K times.

Since the dates of the quarter ranges are always the same (Jan1 - Mar31, Apr1 - Jun30, etc) and the only thing changing is the year, it is faster to just combine the year with the date range.

Here is my new solution:

function getDate_FQ(range)
 var now = new Date();
 var dateArr = 0: ['-01-01', '-03-31'], 1: ['-04-01', '-06-30'], 2: ['-07-01', '-09-30'], 3: ['-10-01', '-12-31']
 switch(range)
 case 'Previous FQ':
 now.setUTCMonth(now.getUTCMonth()-3);
 break;
 case 'Next FQ':
 now.setUTCMonth(now.getUTCMonth()+3);
 break;
 case 'Current FQ':
 break;
 
 var quarter = Math.floor((now.getUTCMonth() / 3));
 var dates = dateArr[quarter]
 var firstDate = (now.getUTCFullYear()) + dates[0];
 var endDate = (now.getUTCFullYear()) + dates[1];
 return([firstDate, endDate])