Function
Description
Examples
Math.trunc(x)
The integral part of x (all
fractional digits removed)
Math
.
trunc
(
7.7
)
// 7
Math
.
trunc
(
-
5.8
)
// -5
Math.round(x)
x rounded to the nearest
integer
Math
.
round
(
7.2
)
// 7
Math
.
round
(
7.7
)
// 8
Math
.
round
(
-
7.7
)
// -8
Math
.
round
(
-
7.2
)
// -7
Math.min(x1, x2,...)
Returns the minimum
argument
Math
.
min
(
1
,
2
)
// 1
Math
.
min
(
3
,
0.5
,
0.66
)
// 0.5
Math
.
min
(
3
,
0.5
,
-
0.66
)
// -0.66
Math.max(x1, x2,...)
Returns the maximum
argument
Math
.
max
(
1
,
2
)
// 2
Math
.
max
(
3
,
0.5
,
0.66
)
// 3
Math
.
max
(
-
3
,
0.5
,
-
0.66
)
// 0.5
Pseudorandom Number Generation
Pseudorandom number generation is provided by
Math.random
, which returns a
pseudorandom number greater than or equal to 0 and less than 1. You may recall
from algebra that number ranges are often denoted with square brackets (inclusive)
and parentheses (exclusive). In this notation,
Math.random
returns numbers in the
range [0, 1).
Math.random
does not provide any convenience methods for providing pseudoran‐
dom numbers in different ranges.
shows some general formulas for getting
other ranges. In this table,
x
and
y
denote real numbers and
m
and
n
denote integers.
Table 16-4. Number pseudorandom number generation
Range
Example
[0, 1)
Math.random()
[x, y)
x + (y-x)*Math.random()
Integer in [m, n)
m + Math.floor((n-m)*Math.random())
Integer in [m, n]
m + Math.floor((n-m+1)*Math.random())
A common complaint about JavaScript’s pseudorandom number generator is that it
can’t be seeded, which is important to testing some algorithms involving pseudoran‐
dom numbers. If you need seeded pseudorandom numbers, see David Bau’s
234 | Chapter 16: Math
