Detect iPhone user agent, offer app download, and javascript redirect to iTunes App Store

ios_detect.coffee

OFFER = 'We have an app available in the App Store! Download now?'
ITUNES_URL = '<Your iTunes URL Here>'

createCookie = (name,value,days) ->
  if days
    date = new Date()
    date.setTime(date.getTime() + (days * 24 * 60 * 60 * 365))
    expires = '; expires=' + date.toGMTString()
  else
    expires = ''
  document.cookie = name + '=' + value + expires + '; path=/';

readCookie = (name) ->
  nameEQ = name + '='
  cookie_array = document.cookie.split(';')
  for value in cookie_array
    value = value.substring(1, value.length) while (value.charAt(0) == ' ')
    return value.substring(nameEQ.length, value.length) if value.indexOf(nameEQ) == 0

$ ->
  if navigator.userAgent.match(/iPhone/i) or navigator.userAgent.match(/iPod/i) or navigator.userAgent.match(/iPad/i)
    if !readCookie('iphoneAdvertised')
      createCookie('iphoneAdvertised', true, 7)
      res = confirm OFFER
      if res
        window.location.replace(ITUNES_URL)

Bobby, any thoughts on my changes below?

userAgentCheck (userAgent) ->
  if userAgent.match(/iPhone/i) or userAgent.match(/iPod/i) or userAgent.match(/iPad/i)
    return true
  else
    return false

$ -> 
  if userAgentCheck(navigator.userAgent)
    if !readCookie('iphoneAdvertised')
      createCookie('iphoneAdvertised', true, 7)
      res = confirm OFFER
      window.location.replace(ITUNES_URL) if res

=) A little better than the original, but if we're going to optimize it to death you could still DRY it out a little more with something like (untested):

userAgentCheck(ios_list) ->
  for ios_agent in ios_agent_list
    return true if navigator.userAgent.match(ios_agent)
  false

$ -> 
  if userAgentCheck([/iPod/i, /iPhone/i, /iPad/i])
    if !readCookie('iphoneAdvertised')
      createCookie('iphoneAdvertised', true, 7)
      res = confirm OFFER
      window.location.replace(ITUNES_URL) if res

I don't know if it makes sense to pass navigator.userAgent since it's accessible from anywhere.

True, good point there. Haven't done any work with detecting / responding to mobile user agent strings so my ideas may not be worth much.