HTML and CSS Reference

In-Depth Information

Figure 11-21

Properties of the Math object

Math
Constant

Description

Math.E

The natural logarithm base,
e
(approximately 2.7183)

Math.LN10

The natural logarithm of 10 (approximately 2.3026)

The natural logarithm of 2 (approximately 0.6931)

Math.LN2

Math.LOG10E

The base 10 logarithm of
e
(approximately 0.4343)

Math.LOG2E

The base 2 logarithm of
e
(approximately 1.4427)

Math.PI

The value

(approximately 3.1416)

p

Math.SQRT1_2

The value of 1 divided by the square root of 2 (approximately 0.7071)

Math.SQRT2

The value of the square root of 2 (approximately 1.4142)

For example, the formula to calculate the volume of a sphere is 4π
r
3
/3, where
r
is the

radius of the sphere. To reference the value of π in the calculation of a sphere's vol-

ume, you would apply the
Math.PI
constant. To cube the value of
r
, you would use the

method
Math.pow(
r
, 3)
. Putting these together, a function to return the volume of a

sphere given the radius is:

function sphereVolume(radius) {

volume = 4*Math.PI*Math.pow(radius, 3)/3;

return volume;

}

To calculate the volume of a sphere that is two units in radius, you could then enter the

expression

var x = sphereVolume(2);

and JavaScript would assign a value of 33.5103 to the
x
variable.

You don't need to use any
Math
object constants for the New Year's Bash Web site.

However, the countdown clock needs to display only the integer portion of the days left

in the year. You can calculate this value using the
Math.floor()
method, which rounds

a value down to the next lowest integer. For the days left value of
310.39…
currently in

the countdown clock, this method returns the integer value
310
. You'll apply this method

to the value displayed in the daysLeft field.

To apply the
Math.floor()
method:

◗

1.
Return to the
clock.htm
file and the NYClock() function in your text editor.

◗

2.
Change the statement that sets the value of the
daysLeft
field to the following two

lines, as shown in Figure 11-22:

// display days rounded to the next lowest integer

document.clockform.daysLeft.value = Math.floor(days) + “ day(s)”;