JavaScript 2.0-The Complete Reference, Second ... - freecodingtutorial

Table 7-4: Methods Provided by the Math Object
Method Returns
Math.tan(arg) Tangent of arg
There are several aspects of the Math object that need to be kept in mind. The trigonometric
methods work in radians, so you need to multiply any degree measurements by / 180 before
using them. Also, because of the imprecise characteristic of floating-point operations, you might
notice minor deviations from the results you expect. For example, though the sine of is 0, the
following code:
alert(Math.sin(Math.PI));
gives the result
This value is very close to zero, but just large enough to trip up sensitive calculations.
It might seem that Math does not provide the capability to compute logarithms in bases other
than e. Indeed it does not, directly. However, the following mathematical identity
loga n = (loge n) / (loge a)
can be used to compute logarithms in an arbitrary base. For example, you can compute the log
base 2 of 64 as
var x = Math.log(64) / Math.log(2);
Random Numbers
Because the Math.random() method returns values between zero and one, you must
normalize its return value to fit the range of numbers required of your application. An easy way
to get random integers in the range m to n (inclusive) is as follows:
Math.round(Math.random() * (n - m)) + m;
So to simulate a die roll you would use
roll = Math.round(Math.random() * (6 - 1)) + 1;
Generating random numbers in this manner is sufficient for most applications, but if ―high
quality‖ randomness is required, a more advanced technique should be used.
Easing Math Computations
When working extensively with the Math object, it is often convenient to use the with
statement. Doing so allows you to use Math properties without prefixing them with ―Math.‖ The
concept is illustrated by the following example (computing the length of a side of a triangle with
the Law of Cosines):
with (Math)
{