I could suppose that there might not be the full support for the full range of Math. functions and constants for standard decimal math as found in implementations of decimal math classes in c++ etc as might be used to implement this (?). that is what I am seeing with the set of functions and methods available for that kind of data type, the actual set of functions supported is rather limited. perhaps it can be limited to some sort of standard subset of C++11 or future c++ standard library thing.

this is needed for financial calculations. as things are now, floating point error really messes up the numbers when you start getting to repeatedly adding and subtracting multiples of 0.11 and you get values like +/-0.009999999999999986
when you should have 0 and , so this kind of ruins things for financial calculations. you can use .toFixed of course, but this does not totally eliminate the problems with floating point. it's successive additions and subtractions of small values like 0.01 or smaller and sometimes even values in the range 0.1 that introduce floating point error into calculations.

JavaScript seems to be a subset of Java data type classes. seeing this, there are some Java classes I can see which seem to fit this need: 
http://docs.oracle.com/javase/7/docs/api/java/math/BigDecimal.html
http://docs.oracle.com/javase/7/docs/api/java/math/BigInteger.html
http://docs.oracle.com/javase/7/docs/api/java/text/DecimalFormat.html
http://docs.oracle.com/javase/7/docs/api/java/text/DecimalFormatSymbols.html
http://docs.oracle.com/javase/7/docs/api/java/text/spi/DecimalFormatSymbolsProvider.html
http://docs.oracle.com/javase/7/docs/api/java/lang/Comparable.html
http://docs.oracle.com/javase/7/docs/api/java/io/Serializable.html
http://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Delayed.html


you will have to decide which interfaces on Comparable you do or don't need, or if you need Comparable at all.


BigDecimal is the only class which seems to do decimal. I had to look at dependencies.

if you want to see the problem in action, play around with various values like 0.11, 0.40, 0.41, 0.42 in http://Jesusnjim.com/calculators/finances/cash-change.html