My JS calculator doesn't work on iPhone

It work fine on my desktop but for some reason it doesn’t work on my iPhone. I’m not sure if it’s just my phone or there’s something I’m missing in my code.
The link is calcjack.surge.sh
Source code is at: github.com/jackhou147/javascriptCalculator
Thank you guys

Nvm guys problem fixed. It seems like IOS doesn’t support the “let” keyword in javascript so I replaced them with “var” and it worked.