How do I undo a function using Javascript?

Question

I have made this amazing calculator until it came to the point where I am facing a problem of having to reset the calculator entirely even if I get one typo which is a major problem. Is there a certain function or piece of code that would do undoing with ease?

Answer 1

if you look for a cheap way to undo the whole code you're hiding the problem,not solving it

Answer 2

Not the entire code but a function. And at this point in time I don't really care about ease.

Answer 3

By the way, how am I hiding the "problem"?

Answer 4

By the way, how am I hiding the "problem"?