How do I return the result of my calculator?

Question

https://code.sololearn.com/WWsM8jajToBX/?ref=app
Every time a number or operator button is pressed, it is added to an array that acts as the memory. The array consists of strings of what the user types in ie [‘3’ , ‘+’ , ‘3’]
Then when the user presses the equal button, I want the array form into one string using the join() method ie [‘3+3]
Then I want to use the eval function to convert it into numbers and return an answer. 3+3 result: 6
But so far the only thing that returns is undefined. Please help.

Answer 1

https://code.sololearn.com/WWsM8jajToBX/?ref=app
Like this?
I think I did what you said correctly, but I must be missing something because it still returns undefined. I’ll keep trying.