Very readable! Helped me reflect on my solution and see a new way of doing things. Thanks :)

i starts as the char code of the first entry, it will increment if it matches in the .map to be the one more (the i++). If it doesnt match at any point then there is a missing letter, and i will stop increasing which will leave i as the char code of the missing letter.

It's useful to go along with pen and paper to see what each operation is doing. Remember that i++ mutates i, and notice that the map is just acting as a forEach here

The peak of human achievement

Yeah. He isn't storing or using the array .map creates. Just iterating over it to conditionally increment i. So that's why I asked why he used .map and not .forEach

forEach: This iterates over a list and applies some operation with side effects to each list member (example: saving every list item to the database)

map: This iterates over a list, transforms each member of that list, and returns another list of the same size with the transformed members (example: transforming list of strings to uppercase)
ref: https://stackoverflow.com/questions/34426458/javascript-difference-between-foreach-and-map

I have a hard time understanding the ternary operator usage here. Could someone please explain this solution in more depth? It just seems so sharp and to the point! I really want to understand this better

wow.. achieving the same result took me 20 lines of code and 2 hours of straining my brain.
I cannot believe this is how smooth the code could be. Lots to learn!!