JavaScript Cookbook

Chapter 3. Dates, Time, and Timers

3.0. Introduction

JavaScript’s date and time functionality is quite extensive, and more than sufficient for most applications.

The Date object contains a number representing the date and time, rather than a string representation. The numeric value for the Date object is the number of seconds since January 01, 1970 UTC. Leap seconds are ignored.

Strings used to create dates are parsed and converted into this numeric value. Older browsers required that this string be UTC (Coordinated Time Universal or Greenwich Mean Time) format. Beginning with ECMAScript 5, ISO 8601 parsing is supported, which I’ll cover later in the chapter.

The Date Object

Dates are managed through the Date object. You can create a date using a variety of techniques (see Recipe 3.1 for a discussion of different approaches), and modify the date using an extensive number of methods.

You can also access every aspect of a date: year, month, day of week, time, and so on, using specialized get and set methods, described in Tables 3-1 and 3-2.

Table 3-1. Date object get methods

Method	Purpose
getDate	Returns day of the month (0–31)
getDay	Returns day of the week (0–6)
getFullYear	Returns 4-digit full year
getHours	Returns local hour (0–23)
getMilliseconds	Returns local milliseconds (0–999)
getMinutes	Returns local minute (0–59)
getMonth	Returns local month (0–11)
getSeconds	Returns local second (0–59)
getTime	Returns number of seconds since January 1, 1970 00:00:00 UTC
getTimezoneOffset	Returns time zone from UTC ...