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




A number.

Return value

The integer 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.

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) {
  var n = x - x%1;
  return n===0 && (x<0 || (x===0 && (1/x !== 1/0))) ? -0 : n;


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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic Support38 (Yes)25 No257.1
FeatureAndroidChrome for AndroidEdge mobileFirefox for AndroidIE mobileOpera AndroidiOS Safari
Basic Support (Yes) (Yes) (Yes)25 No (Yes)8

See also

Document Tags and Contributors

 Last updated by: Phrogz,