mozilla
Your Search Results

    Math.trunc()

    This is an experimental technology, part of the ECMAScript 6 (Harmony) proposal.
    Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future version of browsers as the spec changes.

    Summary

    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

    Example: 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);
    }
    

    Specifications

    Specification Status Comment
    ECMAScript 6 (ECMA-262)
    The definition of 'Math.trunc' in that specification.
    Release Candidate Initial definition.

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support 38 25 (25) Not supported 25 7.1
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support Not supported Not supported 25.0 (25) Not supported Not supported iOS 8

    See also

    Document Tags and Contributors

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