Learning JavaScript

Purposeful Objects: Date and Math

The JavaScript Date and Math objects provide access to the type of functionality you might not think about—until the moment you need it and say to yourself, “I wonder how to...”. They are created for specific purposes—to work with dates or math. No more, no less.

The Date

The Date object can create a date and then access any aspect of it—year, day, second, and so on. Creating a date without passing in any parameters produces a date based on the client machine’s date and time:

var dtNow = new Date(  );

Right at the moment I’m reading this, in St. Louis, Missouri, at 9 p.m. on a Friday (authors have no lives), equals out to:

Fri Apr 07 2006 21:09:14 GMT-0500 (CDT)

You can also pass in parameters to create a specific date. You can enter the number of milliseconds since January 1, 1970 at 12:00:00:

var dtMilliseconds = new Date(5999000920);
document.writeln(dtMilliseconds.toUTCString(  ));

This results in the following date written to the page:

Wed, 11 Mar 1970 10:23:20 GMT

You can also use a string to create a date, if you use the proper format:

var nowDt = new Date("March 12, 1980 12:20:25");

You can forgo the time and just get a date with times set to zeros. You can also pass in each value of the date as integers, in order of year, month (as 0 to 11), day, hour, minutes, seconds, and milliseconds:

var newDt = new Date(1977,12,23);
var newDt = new Date(1977,11,24,19,30,30,30);

Once you have a date, there are several methods you can access, including a few static ...