Hi,
I only managed to solve this Kata with using eval(), but I learned a lot from others' solutions.

You can read why it is not a good thing to use eval() here:
Here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/eval

"Never use eval()!
eval() is a dangerous function, which executes the code it's passed with the privileges of the caller. If you run eval() with a string that could be affected by a malicious party, you may end up running malicious code on the user's machine with the permissions of your webpage / extension. More importantly, a third-party code can see the scope in which eval() was invoked, which can lead to possible attacks in ways to which the similar Function is not susceptible. "