I think what you want I do is same that FCC solution 3. Now that I saw this solution I can’t think whithout thinking of this soluton.
I don’t want to do just a copie.
I give up. 
I have to go further in the next exercises. 
Could you show me how you would have done with the initilizing sum = 0 ?
I wrote that solution, so I would recommend it 
The advanced version of that solution with the initialization on the sum is here
https://forum.freecodecamp.org/t/javascript-performance-measurement-variability/394059
it’s very astonish, to much complicated for me for now.
I know nothing about test of performance.
Thanks for your help, I will try to do the next exercise tomorrow.
It definitely taxes time to learn, but it’s 100% learnable. The solution you wrote is pretty good though!
Nice work and good luck tomorrow!