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




A number.


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).


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


Math.trunc = Math.trunc || function(x) {
  return x < 0 ? Math.ceil(x) : Math.floor(x);


Specification Status Comment
ECMAScript 2015 (6th Edition, ECMA-262)
The definition of 'Math.trunc' in that specification.
Standard Initial definition.
ECMAScript 2017 Draft (ECMA-262)
The definition of 'Math.trunc' in that specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support 38 25 (25) No support 25 7.1
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support 25.0 (25) No support No support 8

See also

Document Tags and Contributors

 Contributors to this page: fscholz, Mingun, ziyunfei, realityking,
 Last updated by: fscholz,