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




A number.

Return value

The integral part of the given number.


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).


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 - x % 1;


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


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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.