Can Anyone explain please why did we write ": [ ] " in line 10. I believe it is the simplest way to write but what exactly is this, can anyone give another example of this to understand please?
you need to look at lines 9 and 10 together. It's just a ?:
conditional operator.
If there are errors - use helper function (it probably flattens various error messages, page level, field level, duplicate rules etc) to get 1 simple error message.
Else return an empty array.