Find letter in a String (charAt)

As said in comments, you don't have to create your own function since indexOf / allMatches / contains are quiet enough for most of case.

And there is no charAt() equivalent since String act as a list of characters. You can use the [] operator to get a letter at a specific index:

'Hello World'[6] //return 'W'

I think

items.indexOf('i');

print(items.indexOf('i')); // prints: 1 because 'i' is found on the 2nd position

is what you are looking for, but you already use it in your question.