How to calculate the number of days between 2 dates in JavaScript
I had this problem: how do I calculate the number of days between 2 dates?
In particular, I wanted to count the number of nights that a person had to pay to rent a house and sleep in it, depending on the checkin date, and the checkout date.
I looked at different solutions, and the one that gave me the least problems, considering all the issues with dates (including DST), was this: starting from the starting date, we add one day until the date represents a date after the end date.
Here’s the code:
const numberOfNightsBetweenDates = (startDate, endDate) => {
const start = new Date(startDate) //clone
const end = new Date(endDate) //clone
let dayCount = 0
while (end > start) {
dayCount++
start.setDate(start.getDate() + 1)
}
return dayCount
}
I first clone the dates we are given, because dates are objects, and we get a reference to that object. This means that using setDate()
in the function would also affect the variable outside of this function - not something we look forward to!
That’s it.
If instead you want to get the number of days between 2 dates (say, today to tomorrow is 2 days), just change while (end > start)
to while (end >= start)
. That would work. Or increase the dayCount
starting point to 1
.
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