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root = exports ? window
class HandlerStack
constructor: ->
@stack = []
@counter = 0
@passDirectlyToPage = new Object() # Used only as a constant, distinct from any other value.
@eventConsumed = new Object() # Used only as a constant, distinct from any other value.
genId: -> @counter = ++@counter
# Adds a handler to the stack. Returns a unique ID for that handler that can be used to remove it later.
push: (handler) ->
handler.id = @genId()
@stack.push handler
handler.id
# Called whenever we receive a key event. Each individual handler has the option to stop the event's
# propagation by returning a falsy value.
bubbleEvent: (type, event) ->
for i in [(@stack.length - 1)..0] by -1
handler = @stack[i]
# We need to check for existence of handler because the last function call may have caused the release
# of more than one handler.
if handler && handler[type]
@currentId = handler.id
passThrough = handler[type].call(@, event)
if not passThrough
DomUtils.suppressEvent(event) if @isChromeEvent event
return false
# If the constant @passDirectlyToPage is returned, then discontinue further bubbling and pass the
# event through to the underlying page. The event is not suppresssed.
if passThrough == @passDirectlyToPage
return false
# If the constant @eventConsumed is returned, then discontinue further bubbling and
# return false.
if passThrough == @eventConsumed
return false
true
remove: (id = @currentId) ->
for i in [(@stack.length - 1)..0] by -1
handler = @stack[i]
if handler.id == id
@stack.splice(i, 1)
break
# The handler stack handles chrome events (which may need to be suppressed) and internal (fake) events.
# This checks whether that the event at hand is a chrome event.
isChromeEvent: (event) ->
event?.preventDefault? and event?.stopImmediatePropagation?
# Convenience wrapper for handlers which always continue propagation.
alwaysPropagate: (handler) ->
handler()
true
# Convenience wrapper for handlers which never continue propagation.
neverPropagate: (handler) ->
handler()
false
root.HandlerStack = HandlerStack
root.handlerStack = new HandlerStack
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