extension/packages/find-link.coffee

   1 utils = require 'utils'
   2
   3 # All the following elements qualify as a link
   4 LINK_ELEMENTS = [
   5   "a"
   6   "area[@href]"
   7   "button"
   8 ]
   9
  10 # All elements that have one or more of the following properties
  11 # qualify as a link
  12 LINK_ELEMENT_PROPERTIES = [
  13   "@onclick"
  14   "@onmousedown"
  15   "@onmouseup"
  16   "@oncommand"
  17   "@role='link'"
  18   "@role='button'"
  19   "contains(@class, 'button')"
  20 ]
  21
  22 # Find a link that match with the patterns
  23 findLinkMatchPattern = (document, patterns) ->
  24   links = getLinkElements(document)
  25   candidateLinks = []
  26
  27   # filter visible links that contain patterns and put in candidateLinks
  28   for i in [0...links.snapshotLength] by 1
  29     link = links.snapshotItem(i)
  30
  31     if isVisibleElement(link) and isElementMatchPattern(link, patterns)
  32       candidateLinks.push(link)
  33
  34   return if candidateLinks.length == 0
  35
  36   for link in candidateLinks
  37     link.wordCount = link.textContent.trim().split(/\s+/).length
  38
  39   # favor shorter links, links near the end of a page
  40   candidateLinks = candidateLinks.sort (a, b) ->
  41     if a.wordCount == b.wordCount then 1 else a.wordCount - b.wordCount
  42
  43   # match patterns
  44   for pattern in patterns
  45     # if the pattern is a word, wrapped it in word boundaries.
  46     # thus we won't match words like 'previously' to 'previous'
  47     exactWordRegex =
  48       if /^\b|\b$/.test(pattern)
  49         new RegExp('\\b' + pattern + '\\b', 'i')
  50       else
  51         new RegExp(pattern, 'i')
  52
  53     for candidateLink in candidateLinks
  54       if exactWordRegex.test(candidateLink.textContent)
  55         return candidateLink
  56
  57
  58 # Returns elements that qualify as links
  59 getLinkElements = do ->
  60   elements = [
  61     LINK_ELEMENTS...
  62     "*[#{ LINK_ELEMENT_PROPERTIES.join(' or ') }]"
  63   ]
  64
  65   return utils.getDomElements(elements)
  66
  67
  68 # Determine if the link is visible
  69 isVisibleElement = (element) ->
  70   document = element.ownerDocument
  71   window   = document.defaultView
  72
  73   # element that isn't visible on the page
  74   computedStyle = window.getComputedStyle(element, null)
  75   if computedStyle.getPropertyValue('visibility') != 'visible' or
  76       computedStyle.getPropertyValue('display') == 'none' or
  77       computedStyle.getPropertyValue('opacity') == '0'
  78     return false
  79
  80   # element that has zero dimension
  81   clientRect = element.getBoundingClientRect()
  82   if clientRect.width == 0 or clientRect.height == 0
  83     return false
  84
  85   return true
  86
  87
  88 # Determine if the link has a pattern matched
  89 isElementMatchPattern = (element, patterns) ->
  90   for pattern in patterns
  91     if element.textContent.toLowerCase().contains(pattern)
  92       return true
  93
  94   return false
  95
  96 exports.find = findLinkMatchPattern