Math.ceil, floor, and trunc Examples¶Math.ceil¶The general syntax for this method is:
Math.ceil(number)
This method rounds a decimal value UP to the next integer (hence the ceiling reference in the name). Integer values remain the same.
ceil also operates on arrays (see below).
Numerical strings can also be evaluated, but should be avoided as a best practice.
Example
1console.log(Math.ceil(8.88));
2
3console.log(Math.ceil(8.1));
4
5console.log(Math.ceil(-3.9));
6
7console.log(Math.ceil(5));
Console Output
9
9
-3
5
Math.floor¶The general syntax for this method is:
Math.floor(number)
This method is the opposite of Math.ceil. It rounds a decimal value DOWN to
the previous integer. Integer values remain the same.
floor also operates on arrays (see below).
Numerical strings can also be evaluated, but should be avoided as a best practice.
Example
1console.log(Math.floor(8.88));
2
3console.log(Math.floor(8.1));
4
5console.log(Math.floor(-3.9));
6
7console.log(Math.floor(5));
Console Output
8
8
-4
5
Math.trunc¶The general syntax for this method is:
Math.trunc(number)
This method removes any decimals and returns only the integer part of number.
trunc also operates on arrays (see below).
Numerical strings can also be evaluated, but should be avoided as a best practice.
Example
1console.log(Math.trunc(8.88));
2
3console.log(Math.trunc(10.000111));
Console Output
8
10
Note
At first glance, Math.floor and Math.trunc appear to do exactly the
same thing. However, a closer look shows that the two methods treat negative numbers
differently.
Console Output
map¶When combined with the map array method, ceil, floor, and trunc
will operate on each entry in an array. The syntax for this is:
arrayName.map(Math.method)
Example
1let numbers = [-2, 3.33, -4.44, 8.88];
2
3console.log(numbers.map(Math.ceil));
4console.log(numbers.map(Math.floor));
5console.log(numbers.map(Math.trunc));
Console Output
[ -2, 4, -4, 9 ]
[ -2, 3, -5, 8 ]
[ -2, 3, -4, 8 ]