In the case of currency, it is better to use decimal arithmetic because if you use float numbers the rounding behaves different than doing the same operations by hand or in a calculator. Another option is to use integers (to represent number of cents) and just print the decimal point when displaying the number.
I'm not sure if you're answering my question or not. I've inspected the source of both libraries, and they both use the JS method toFixed().
Never mind, you are right it is just to format decimals.
I'm not sure that it does the same job.
As stated in the blog, the Formspider framework had a Java renderer that uses DecimalFormat and we needed the same functionality on the javascript side which means formatting numbers with variable masks such as "$#,#00.0#" or "00.0##%" that is defined by the user. So sprintf is not the same.
By the way, this code was wrtiten in 2008.