Split values in a string?

General
12

First, please don't post code as an image. Use the method described in How to share code or flow json. That would have saved me having to type out bits of the code again.

Change
let data = ""
which initialises data to an empty string so that when you add the other ones it concatenates the text rather than adding the numbers
to
let data = 0

In fact even better would be to use Array method reduce(). See Array.prototype.reduce() - JavaScript | MDN