The result of the computation 1/3 in JS results in a number which is terminating, but that number is not 1/3. Open up your console and type 1/3+1/3+1/3... 1, as expected. Then type 1-1/3-1/3-1/3... I get about 1e-16, which is not 0.

The statement that "1/3 is terminating" is not true in binary, it is not true in decimal, and the only reason that you sometimes get the expected results is that sometimes the rounding errors will cancel out.