How to get a given date in every month in javascript?

Question

I need to find this month, previous month and next month of a specific date.

For example, the date was set to 31 months, which I expect to receive on 2018-02-28, 2018-03-31 and 2018-04-30. For those dates that do not have 31 than the next day.

And finally, generate 2 periods, 2018-02-28 - 2018-03-29, 2018-03-30 - 2018-04-31. I don't know how to handle feb and a month that is less than 31.

var d = new Date(); var tyear = d.getFullYear(); //2018 var tmonth = d.getMonth(); //2 new Date(2018, tmonth-1, 31);//output 2018-03-02 not what I wanted 

Answer 1

I think you need an array with 12 numbers in it. Each number is the number of days in each month, and the numbers in the array are in order (the first number is 31 because January has 31 days, the second is 28 or 29 for February), etc. Then you will get the month number from the date of entry and look in the array the number corresponding to the month number +/-.

Then you will need to create a date for the previous month and next month depending on the number of days in the current month.

See comments on line:

 let daysInMonths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; document.getElementById("date").addEventListener("input", function(){ console.clear(); // Create new Date based on value in date picker var selectedDate = new Date(this.value + 'T00:00'); var year = selectedDate.getYear(); // Determine if it is a leap year (Feb has 29 days) and update array if so. if (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)) { daysInMonths[1] = 29; } var selectedDateMonth = selectedDate.getMonth(); // Get previous month number (if current month is January, get December) let prevMonth = selectedDateMonth > 0 ? selectedDateMonth - 1 : 11; let prevMonthDate = null; // If selected date is last day of month... if(selectedDate.getDate() === daysInMonths[selectedDateMonth]){ // Create new date that takes the selected date and subtracts the correct amount of // days from it based on a lookup in the array. var newDate1 = new Date(selectedDate.getTime()); prevMonthDate = new Date(newDate1.setDate(selectedDate.getDate() - daysInMonths[selectedDateMonth])); } else { // Create a new date that is last month and one day earlier var newDate2 = new Date(selectedDate.getTime()); prevMonthDate = new Date(new Date(newDate2.setDate(selectedDate.getDate() - 1)) .setMonth(selectedDate.getMonth() - 1)); } // Get next month (if current month is December, get January let nextMonth = selectedDateMonth < 11 ? selectedDateMonth + 1 : 0; let nextMonthDate = null; // Same idea for next month, but add instead of subtract. // If selected date is last day of month... if(selectedDate.getDate() === daysInMonths[selectedDateMonth]){ var newDate3 = new Date(selectedDate.getTime()); nextMonthDate = new Date(newDate3.setDate(selectedDate.getDate() + daysInMonths[selectedDateMonth + 1])); } else { var newDate4 = new Date(selectedDate.getTime()); nextMonthDate = new Date(new Date(newDate4.setDate(selectedDate.getDate() + 1)).setMonth(selectedDate.getMonth() + 1)); } console.log("Last month date: " + prevMonthDate.toLocaleDateString()); console.log("Next month date: " + nextMonthDate.toLocaleDateString()); }); 

 <p>Pick a date: <input type="date" id="date"></p> 

Answer 2

Use this approach:

Javascript Date Object - Adding and Subtracting Months

From the author

There is a slight problem with the Javascript Date() object when trying to move to the next month or return to the previous month.

For example, if your date is set to October 31, 2018 and you add one month, you probably expect the new date to be November 30, 2018, since November 31 does not exist. This, however, is not the case.

Javascript automatically promotes your Date object until December 1st. This function is very useful in most situations (i.e., adding days to a date, determining the number of days in a month or if it is a leap year), but not for adding / subtracting months. I have compiled some functions below that extend the Date() object: nextMonth() and prevMonth() .

 function prevMonth() { var thisMonth = this.getMonth(); this.setMonth(thisMonth - 1); if (this.getMonth() != thisMonth - 1 && (this.getMonth() != 11 || (thisMonth == 11 && this.getDate() == 1))) this.setDate(0); } function nextMonth() { var thisMonth = this.getMonth(); this.setMonth(thisMonth + 1); if (this.getMonth() != thisMonth + 1 && this.getMonth() != 0) this.setDate(0); } Date.prototype.nextMonth = nextMonth; Date.prototype.prevMonth = prevMonth; var today = new Date(2018, 2, 31); //<----- March 31st, 2018 var prevMonth = new Date(today.getTime()); prevMonth.prevMonth(); console.log("Previous month:", prevMonth); console.log("This month:", today) var nextMonth = new Date(today.getTime()); nextMonth.nextMonth(); console.log("Next month:", nextMonth); 

 .as-console-wrapper { max-height: 100% !important; top: 0; } 

Answer 3

Dates and time zones are a real pain in JS, so the challenge is accepted.

I broke it in two steps:
- Count the days of the previous and next month
- Compare with the selected day and select the smallest number

Included Testers

 function createUTCDate(year, month, day) { return new Date(Date.UTC(year, month, day)); } function splitDate(date) { return { year: date.getUTCFullYear(), month: date.getUTCMonth(), day: date.getUTCDate() }; } function numberOfDaysInMonth(year, month) { return new Date(year, month + 1, 0).getDate(); } function dateNextMonth(dateObj) { const daysNextMonth = numberOfDaysInMonth(dateObj.year, dateObj.month + 1); const day = Math.min(daysNextMonth, dateObj.day); return createUTCDate(dateObj.year, dateObj.month + 1, day); } function datePreviousMonth(dateObj) { const daysPrevMonth = numberOfDaysInMonth(dateObj.year, dateObj.month - 1); const day = Math.min(daysPrevMonth, dateObj.day); return createUTCDate(dateObj.year, dateObj.month - 1, day); } const log = console.log; function print(dateString) { const date = new Date(dateString); const dateObj = splitDate(date); log("Previous: ", datePreviousMonth(dateObj).toISOString()); log("Selected: ", date.toISOString()); log("Next: ", dateNextMonth(dateObj).toISOString()); log("--------------"); } const testCases = [ "2018-03-01 UTC", "2018-03-31 UTC", "2018-01-01 UTC", "2018-12-31 UTC" ]; testCases.forEach(print); 

Please note that hacking with new Date(xxx + " UTC") does not meet the specification and is simply intended for testing. Results may vary for each browser. You must choose an input format and create your dates accordingly.

Answer 4

A simple algorithm is to add months to the original date, and if the new date is incorrect, set it on the last day of the previous month. Saving the original date values ​​is unmodified, for example,

 /* @param {Date} start - date to start ** @param {number} count - number of months to generate dates for ** @returns {Array} monthly Dates from start for count months */ function getMonthlyDates(start, count) { var result = []; var temp; var year = start.getFullYear(); var month = start.getMonth(); var startDay = start.getDate(); for (var i=0; i<count; i++) { temp = new Date(year, month + i, startDay); if (temp.getDate() != startDay) temp.setDate(0); result.push(temp); } return result; } // Start on 31 Jan in leap year getMonthlyDates(new Date(2016,0,31), 4).forEach(d => console.log(d.toString())); // Start on 31 Jan not in leap year getMonthlyDates(new Date(2018,0,31), 4).forEach(d => console.log(d.toString())); // Start on 30 Jan getMonthlyDates(new Date(2018,0,30), 4).forEach(d => console.log(d.toString())); // Start on 5 Jan getMonthlyDates(new Date(2018,0,5), 4).forEach(d => console.log(d.toString())); 

Answer 5

I handle it stupidly, concatenating a string

 let daysInMonths = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]; let months = ["01", "02", "03", "04", "05", "06", "07", "08", "09", "10", "11", "12"]; var target = nexttarget = lasttarget = "29"; //target day if (((year % 4 === 0) && (year % 100 !== 0)) || (year % 400 === 0)) { daysInMonths[1] = 29; } function findLastDay(target, month){ if(target > daysInMonths[month]){ target = daysInMonths[month]; } return target; } 

then

 var d = new Date(); var year = d.getFullYear(); var month = d.getMonth(); target = findLastDay(target, month); var this_month = year+"-"+months[month]+"-"+target; console.log(this_month);//2018-03-29 // next month if(month == 11){ nextmonth = 0; nextyear = year + 1; }else{ nextmonth = month+1; nextyear = year; } nexttarget = findLastDay(nexttarget, nextmonth); var next_month = nextyear+"-"+months[nextmonth]+"-"+nexttarget; console.log(next_month);//2018-04-29 //last month if(month == 0){ lastmonth = 11; lastyear = year - 1; }else{ lastmonth = month - 1; lastyear = year; } lasttarget = findLastDay(lasttarget, lastmonth); var last_month = lastyear+"-"+months[lastmonth]+"-"+lasttarget; console.log(last_month);//2018-02-28 

Answer 6

Data processing is difficult in the best of times. Do not do it yourself. Use Moment.js .

 var target = 31; var today = moment().date(target).calendar(); // today == '03/31/2018' var nextMonth = moment().date(target).add(1, 'month').calendar(); // nextMonth == '04/30/2018' var lastMonth = moment().date(target).subtract(1, 'month').calendar() // lastMonth == '02/28/2018'