For when you can't remember the difference between .each and .map, here's a reminder! It's written in Ruby, but the principle is the same in Javascript.

each-vs-map.rb

# In Ruby

# Array.each
# Iterate through each a collection unchanged

User.all.each do |user|
  puts user.email
  puts user.name
  puts
end

# => [email protected]
# => Shane Becker 
# => 
# => [email protected]
# => Aki Braun
# => 

# Array.map
# Create a new collection by manipulating an original collection
# Optionally, iterate over the new one

emails = User.all.map{ |u| u.email }
puts emails

# => ["[email protected]", "[email protected]"]

emails.each do |email|
  puts email 
end

# => [email protected]
# => [email protected]