Time and Date Manipulation

Working with times and dates can be tricky in programming languages. For this reason, most languages have some sort of built-in Date object that helps to make the process easier. JavaScript is no exception, and we’ll be taking a look at how that works.

The UNIX epoch

The UNIX epoch is an arbitrary date of January 1, 1970 which is used in programming as a reference point in time from which to measure dates. This allows dates to be expressed as an integer that represents the number of seconds since the epoch. As we can imagine, this produces some very large numbers, and there’s a potential problem looming in 2038 when the number of seconds since the epoch will be greater than $2,147,483,647$, which is the maximum value that some programming languages can deal with. Fortunately, JavaScript will be fine, as it can handle bigger values than this.

Times and dates

Date objects contain information about dates and times. Each object represents a single moment in time.

In JavaScript, we can use a constructor function to create a new Date object using the new operator. Try entering the following code:

The variable today now points to a Date object. To see what the date is, we can use the toString() method that all objects have:

If an argument isn’t supplied, the date will default to the current date and time based on the system clock and time zone setting. This means that it can be manipulated and shouldn’t be relied on as an accurate representation of the actual date.

It’s possible to create Date objects for any date by supplying it as an argument to the constructor function. This can be written as a string in a variety of forms, as can be seen in the examples of different holiday dates below:

As we can see, the string passed to the Date constructor can be in a variety of formats. However, in order to be more consistent, we’d recommend ...