HTML and CSS Reference
In-Depth Information
EXPLANATION
1
The function called
weekDay()
is defined.
2
The variable
now
is assigned a number representing the day of the week, where 0
is Sunday.
3
A new
Array
object called
names
is created. It will contain seven elements. Each
element will be assigned the name of the weekday (e.g.,
“Sunday”)
.
4
The value in
now
, a number between 0 and 6, will be used as an index in the
names
array. If
now
is 6, then the value of
names[6]
,
“Saturday”
, will be returned.
5
A
prototype
method called
DayOfWeek
is assigned the name of the function
week-
Day
. Now the
Date
object has a new method that will be inherited by all objects
created from the
Date()
constructor. The capabilities of the
Date
object have been
extended to provide a method that will return the name of the weekday. (See
Chapter 8 for more on prototypes.)
6
A new
Date
object is created with the
Date()
constructor function.
7
The new prototype method is called, and returns the string value of today's date,
“Saturday”
(see Figure 9.23).
Figure 9.23
The day is converted to a string using a prototype.
The
Math
object allows you to work with more advanced arithmetic calculations, such
as square root, trigonometric functions, logarithms, and random numbers, than are pro-
vided by the basic numeric operators. If you are doing simple calculations, you really
won't need it.
Unlike other objects, you don't have to create an instance of the
Math
object with the
new
keyword. It is a built-in object and has a number of properties (see Table 9.5) and
methods (see Table 9.6). The
Math
object always starts with an uppercase M.
Table 9.5
Math
Object Properties
Property
Value
Description
Math.E
2.718281828459045091
Euler's constant, the base of
natural logarithms
Math.LN2
0.6931471805599452862
Natural log of 2
Math.LN10
2.302585092994045901
Natural log of 10
Continues
