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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.

Description

Unlike other three Math methods: Math.floor(), Math.ceil() and Math.round(), the way Math.trunc() works is very simple and straightforward, just truncate the dot and the digits behind it, no matter whether the argument is a positive number or a negative number.

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

Note, 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 < 0 ? Math.ceil(x) : Math.floor(x);
}

  Created by Mozilla Contributors, license: CC-BY-SA 2.5