Find the number of days in a month using JavaScript

Working with dates is admittedly hard, especially in JavaScript where the Date object is not the most intuitive. However, calculating the number of days in a month for a given year is a common task, and can be done with a single line of code.

Date.prototype.getDate() returns the numeric representation of the day of the month, which can be used to calculate the number of days in a month. By setting the days parameter to 0, we can get the last day of the previous month. This effectively allows us to get the number of days in the given month, as months are zero-indexed.

Putting everything together, we can use the Date() constructor to create a date from the given year and month, and then use Date.prototype.getDate() to return the number of days in the given month.

const daysInMonth = (year, month) => new Date(year, month, 0).getDate();

daysInMonth(2020, 12); // 31
daysInMonth(2024, 2); // 29