给定选定的年份，我需要在 JavaScript 中计算该年的第一天和最后一天

Question

Given a selected year, for example: "2020". I need to calculate with JavaScript the first and the last day of the selected year in format: "2020-01-01" and "2020-12-31"

Can someone help me with this? It will be possible doing it with Moment.js? Thanks in advance.

Answer 1

You can achieve it in this simple way

 var formatDate = function(year, month, day) { if (month < 10) month = '0' + month; if (day < 10) day = '0' + day; return [year, month, day].join('-'); } var printDate = function(year){ console.log("Frist day: " + formatDate(year, 1, 1)); console.log("Last day: " + formatDate(year, 12, 31)); } printDate(2020);

Answer 2

I think the easiest and fastest approach is to not "calculate" anything. You don't need to.

function firstOfYear(year) {
  return `${year}-01-01`;
}

function lastOfYear(year) {
  return `${year}-12-31`;
}

const start = firstOfYear(2020); // 2020-01-01
const end = lastOfYear(2020); // 2020-12-31

You might not even need the functions, depending on your use case.

These functions aren't especially reusable, so if you have other dates you'd like to format then some of the other answers provided will be more flexible. But if all you need to do is get the first and last of the year, then I recommend you keep it simple.

Answer 3

 CalculateDates = function(year){ console.log('first day: ' + new Date(year, 0, 1, 4).toJSON().split('T')[0]); console.log('last day: ' + new Date(year, 12, 0, 4).toJSON().split('T')[0]); } CalculateDates(2019)