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

console.log(Math.ceil(8.88));

console.log(Math.ceil(8.1));

console.log(Math.ceil(-3.9));

console.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

console.log(Math.floor(8.88));

console.log(Math.floor(8.1));

console.log(Math.floor(-3.9));

console.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

console.log(Math.trunc(8.88));

console.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

Combine with 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

let numbers = [-2, 3.33, -4.44, 8.88];

console.log(numbers.map(Math.ceil));
console.log(numbers.map(Math.floor));
console.log(numbers.map(Math.trunc));

Console Output

[ -2, 4, -4, 9 ]
[ -2, 3, -5, 8 ]
[ -2, 3, -4, 8 ]