Math.trunc()

The Math.trunc() function returns the integral part of a number by removing any fractional digits.

Syntax

Math.trunc(x)

Parameters

x

A number.

Return value

The integral part of the given number.

Description

Unlike the other three Math methods: Math.floor(), Math.ceil() and Math.round(), the way Math.trunc() works is very simple. It truncates (cuts off) the dot and the digits to the right of it, no matter whether the argument is a positive or negative number.

If the argument is a positive number, Math.trunc() is equivalent to Math.floor(); otherwise Math.trunc() is equivalent to Math.ceil().

The argument passed to this method will be converted to number type implicitly.

Because trunc() is a static method of Math, you always use it as Math.trunc(), rather than as a method of a Math object you created (Math is not a constructor).

Examples

Using Math.trunc()

Math.trunc(13.37);    // 13
Math.trunc(42.84);    // 42
Math.trunc(0.123);    //  0
Math.trunc(-0.123);   // -0
Math.trunc('-1.123'); // -1
Math.trunc(NaN);      // NaN
Math.trunc('foo');    // NaN
Math.trunc();         // NaN

Polyfill

Math.trunc = Math.trunc || function(x) {
  return x - x % 1;
}

Specifications

Browser compatibility

See also

• Math.abs()
• Math.ceil()
• Math.floor()
• Math.round()
• Math.sign()