JavaScript: The Definitive Guide, Fourth Edition

The Date Object

The previous sections have described all of the fundamental data types supported by JavaScript. Date and time values are not one of these fundamental types, but JavaScript does provide a class of object that represents dates and times and can be used to manipulate this type of data. A Date object in JavaScript is created with the new operator and the Date( ) constructor (the new operator will be introduced in Chapter 5, and we’ll learn more about object creation in Chapter 8):

var now = new Date(  );  // Create an object holding the current date and time.
// Create a Date object representing Christmas.
// Note that months are zero-based, so December is month 11!
var xmas = new Date(2000, 11, 25);

Methods of the Date object allow you to get and set the various date and time values and to convert the Date to a string, using either local time or GMT time. For example:

xmas.setFullYear(xmas.getFullYear(  ) + 1);  // Change the date to next Christmas.
var weekday = xmas.getDay(  );  // Christmas falls on a Tuesday in 2001.
document.write("Today is: " + now.toLocaleString(  ));  // Current date/time.

The Date object also defines functions (not methods; they are not invoked through a Date object) to convert a date specified in string or numeric form to an internal millisecond representation that is useful for some kinds of date arithmetic.

You can find full documentation on the Date object and its methods in the core reference section of this book.