The in operator in js is quite different from python: it is used to check if something is actually a property of an object ( here is a link: in operator in js - Flavio Copes )
If you want to check if an element is included in an Array you can use the includes method; something like if ( arr.includes(str[i]) ) ^^
I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.
See this post to find the backtick on your keyboard. The “preformatted text” tool in the editor (</>) will also add backticks around text.