Hi @amcsi,
The for_each argument is used in resources in order to create multiple instances of that resource, but locals is not a block which can be repeated in that manner, and has no for_each argument.
What you are looking for are for expressions. While you cannot create multiple locals from a single expressions, you can for example create a list of maps assigned to a single local value with the structure in your example like so:
locals {
hey = [for f in fileset("${path.module}/functions", "*.js") :
{
value = f
something_else = "additional: ${f}"
}
]
}