flymis/WebRoot/dojojs/src/Deferred.js

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/*
	Copyright (c) 2004-2006, The Dojo Foundation
	All Rights Reserved.

	Licensed under the Academic Free License version 2.1 or above OR the
	modified BSD license. For more information on Dojo licensing, see:

		http://dojotoolkit.org/community/licensing.shtml
*/

dojo.provide("dojo.Deferred");
dojo.require("dojo.lang.func");

dojo.Deferred = function(/* optional */ canceller){
	/*
	NOTE: this namespace and documentation are imported wholesale 
		from MochiKit

	Encapsulates a sequence of callbacks in response to a value that
	may not yet be available.  This is modeled after the Deferred class
	from Twisted <http://twistedmatrix.com>.

	Why do we want this?  JavaScript has no threads, and even if it did,
	threads are hard.  Deferreds are a way of abstracting non-blocking
	events, such as the final response to an XMLHttpRequest.

	The sequence of callbacks is internally represented as a list
	of 2-tuples containing the callback/errback pair.  For example,
	the following call sequence::

		var d = new Deferred();
		d.addCallback(myCallback);
		d.addErrback(myErrback);
		d.addBoth(myBoth);
		d.addCallbacks(myCallback, myErrback);

	is translated into a Deferred with the following internal
	representation::

		[
			[myCallback, null],
			[null, myErrback],
			[myBoth, myBoth],
			[myCallback, myErrback]
		]

	The Deferred also keeps track of its current status (fired).
	Its status may be one of three things:

		-1: no value yet (initial condition)
		0: success
		1: error

	A Deferred will be in the error state if one of the following
	three conditions are met:

		1. The result given to callback or errback is "instanceof" Error
		2. The previous callback or errback raised an exception while
		   executing
		3. The previous callback or errback returned a value "instanceof"