The README in the github JS port has 9000 lines of documentation and code samples (R and JS side by side) to prove the output is the same for all functions.
R is fudging numbers? I dont think so, neither does JS or excel btw.
R shows limited precision to a human, you can control this with options('digits'=22) Example
> options(digits=22)
> 1/1.2
[1] 0.83333333333333337
> options(digits=4)
> 1/1.2
[1] 0.8333