[umanwizard]

25 nanoseconds is much longer than a normal double-precision addition, loop counter increment, and conditional jump back to the top of a loop should take, so there's something other than the time taken by additions that's going on in your benchmark. I'm not a Node.JS expert, but I suspect it's not getting JITted properly, or getting poorly optimized if so.

I tried in C:

    #include <math.h>
    #include <stdio.h>
    int main()
    {
      double a = pow(2, 100);
      for (double i = 0; i < 1e7; ++i) {
        a += i;
      }
      printf("%f\n", a);
    }

and timed it. The time taken was 17ms.