Maybe I'm wrong (hope I'm not), I don't remember any mentions about an array type at that point of the book. I've tried to find it, but I found nothing. It might be an artefact of the original book (the 1st edition).
So I'd replace the "As mentioned earlier" part with something not confusing. I'm not a native English, so probably you have a better idea for the replacement.
Maybe I'm wrong (hope I'm not), I don't remember any mentions about an array type at that point of the book. I've tried to find it, but I found nothing. It might be an artefact of the original book (the 1st edition).
So I'd replace the "As mentioned earlier" part with something not confusing. I'm not a native English, so probably you have a better idea for the replacement.
"I already searched for this issue"
Edition: 2nd
Book Title: You Don't Know JS Yet: Get Started
Chapter: 2
Section Title: Values
Topic: Arrays And Objects