Get the location of an @reply symbol in a string

gistfile1.coffee

# Implementation for a plugin that allows vaguely-Tweetbot-style @mention autofills.
# Finds the index of the @ symbol that should trigger a mention: the @ closest to the typing cursor
# that is preceded by a non-word character or the beginning of the string
#
# "@dave hey"
#  ^
#
# "@john, I thought you should talk to @tony"
#                                      ^
#
# "john@internet.com is his email address (@dave should know it)
#                                          ^

$textarea

search_in = $textarea.val().slice(0, $textarea[0].selectionStart)
regex = /(^|[\W])@/gi

while (sym = regex.exec(search_in))
  at_symbol = if sym.index == 0 then sym.index else sym.index + 1