Returns a lambda that can match an
element against the nth-child pseudo class, given the following arguments:
a — Value of a part.
b — Value of b part.
of_type — True to test only elements of this type (of-type).
reverse — True to count in reverse order (last-).
# File actionpack/lib/action_controller/vendor/html-scanner/html/selector.rb, line 717
def nth_child(a, b, of_type, reverse)
# a = 0 means select at index b, if b = 0 nothing selected
return lambda { |element| false } if a == 0 && b == 0
# a < 0 and b < 0 will never match against an index
return lambda { |element| false } if a < 0 && b < 0
b = a + b + 1 if b < 0 # b < 0 just picks last element from each group
b -= 1 unless b == 0 # b == 0 is same as b == 1, otherwise zero based
lambda do |element|
# Element must be inside parent element.
return false unless element.parent && element.parent.tag?
index = 0
# Get siblings, reverse if counting from last.
siblings = element.parent.children
siblings = siblings.reverse if reverse
# Match element name if of-type, otherwise ignore name.
name = of_type ? element.name : nil
found = false
for child in siblings
# Skip text nodes/comments.
if child.tag? && (name == nil || child.name == name)
if a == 0
# Shortcut when a == 0 no need to go past count
if index == b
found = child.equal?(element)
break
end
elsif a < 0
# Only look for first b elements
break if index > b
if child.equal?(element)
found = (index % a) == 0
break
end
else
# Otherwise, break if child found and count == an+b
if child.equal?(element)
found = (index % a) == b
break
end
end
index += 1
end
end
found
end
end
