JS problem with adding dates dates to all months with 31 days

I am trying to take in a date and get the Javascript to verify which quarter that date is in then output the date 1st day of the next quarter.

My code works except for when someone enters the last day of the month on dates that end on the 31st. I figured out this may have something to do with timezones so I get UTC values instead of actual values so I remove the timezone out of the equation.

//get the last completed date entered.
var strDate = $(‘#view_1639-field_812’).val();

let chosenFreq = $(‘#kn-input-field_838 input[type=radio]:checked’ ).closest(‘label’).text().trim()

	 // verify that we have a frequency
	 if (chosenFreq !="") {
			//verify if strDate is empty
			if (strDate != "") {
				//Break date down into components
				const [month, day, year] =strDate.split("/")
                                  // create a new date object with dates compensate for 0 based month
				let fullDate = new Date (Date.UTC(year, parseInt(month)-1,day))

			     // Get next maintenance date (private funcation see below)
			    let newDate = GetNewDate(fullDate, chosenFreq)

                                     //output date returned from function
				console.log('set new date field' + newDate)

                                    // set date in document
				document.getElementById('view_1639-field_847').value = newDate.toLocaleDateString()

Gets a new date based on the frequency and date passed in /
function GetNewDate(currDate, frequency) {

//verify you have a frequency string
if (frequency != '') {
          //verify we have a date object
	if (Object.prototype.toString.call(currDate) === "[object Date]") {
		dateDay = new Date(currDate).getUTCDate();
		dateMonth = new Date(currDate).getUTCMonth();
		dateYear = new Date(currDate).getUTCFullYear();
			case 'Every 2 years':
				currDate.setFullYear(currDate.getFullYear() + 2)
				if (currDate.getMonth() > 1) {
			case 'Every 3 weeks':
				currDate.setDate(currDate.getDay() + 21)
                            case 'Every 5 years':
				currDate.setFullYear(currDate.getFullYear() + 5)
				if (currDate.getMonth() > 1) {
			case 'Yearly':
				currDate.setFullYear(currDate.getFullYear() + 1)
				if (currDate.getMonth() > 1) {
			case 'Every quarter':
			// Get the month of the year as a number (0-11) 
			const strYear = currDate.getUTCFullYear();
			const q1Date = new Date (strYear + '/03/31')
			const q2Date = new Date (strYear + '/06/30')
			const q3Date = new Date (strYear + '09/30')
			// Calculate the quarter of the year 
			if (currDate <= q1Date) { 
					console.log('first Quarter')
			} else if (currDate <= q2Date) { 
						console.log('second Quarter')
			} else if (currDate <= q3Date) { 
				  console.log('Third Quarter')
		  } else { 
					console.log('fourth Quarter')
					currDate.setUTCFullYear(currDate.getFullYear() + 1);


return currDate


For anyone who wants to know the solution… I have finally made the code work.

As predicted the issue stems from the UTC and the computer’s local timezone. To understand more about the issue watch the following YouTube video on the subject. https://www.youtube.com/watch?v=oKFb2Us9kmg This developer dives into how the Date object works to explain what is happening.

In short, when you pars a date string into a date the date itself is stored in the date object however the time is modified based on the PC’s local timezone which can affect the actual date itself.

So to counter this I added the following line of code which adds back the time to may date value equivalent to my offset.

fullDate.setMinutes(fullDate.getMinutes() + fullDate.getTimezoneOffset())

There were some conversations regarding leap years and the getTimezoneOffset() function. For my application I don’t think this will be a problem as I am only really trying to determine yearly quarters so look into this if you are looking for more precise date manipulation.