javascript 支持链式调用的异步调用框架Async.Operation

Async = {}; 
Async.Operation = function(options) { 
options = options || {}; 
var callbackQueue = []; 
var chain = (options.chain && options.chain === true) ? true : false; 
var started = false; 
var innerChain = null; 
this.result = undefined; 
this.state = "running"; 
this.completed = false; 
this.yield = function(result) { 
var self = this; 
if (!chain) { 
self.result = result; 
self.state = "completed"; 
self.completed = true; 
} else { 
started = true; 
self.result = result; 
self.state = "chain running"; 
self.completed = false; 
} 
setTimeout(function() { 
if (!innerChain) { 
while (callbackQueue.length > 0) { 
var callback = callbackQueue.shift(); 
if (chain) { 
callbackResult = callback(self.result); 
self.result = callbackResult; 
if (callbackResult && callbackResult instanceof Async.Operation) { 
innerChain = Async.chain(); 
while (callbackQueue.length > 0) { 
innerChain.next(callbackQueue.shift()); 
} 
innerChain.next(function(result) { 
self.result = result; 
self.state = "completed"; 
self.completed = true; 
return result; 
}); 
callbackResult.addCallback(function(result) { 
self.result = result; 
innerChain.go(result); 
}); 
} 
} else { 
callback(self.result); 
} 
} 
if (!innerChain) { 
self.state = "completed"; 
self.completed = true; 
} 
} else { 
while (callbackQueue.length > 0) { 
innerChain.next(callbackQueue.shift()); 
} 
innerChain.next(function(result) { 
self.result = result; 
self.state = "completed"; 
self.completed = true; 
return result; 
}); 
} 
}, 1); 
return this; 
}; 
this.go = function(initialArgument) { 
return this.yield(initialArgument); 
} 
this.addCallback = function(callback) { 
callbackQueue.push(callback); 
if (this.completed || (chain && started)) { 
this.yield(this.result); 
} 
return this; 
}; 
this.next = function(nextFunction) { 
return this.addCallback(nextFunction); 
}; 
}; 
Async.chain = function(firstFunction) { 
var chain = new Async.Operation({ chain: true }); 
if (firstFunction) { 
chain.next(firstFunction); 
} 
return chain; 
}; 
Async.go = function(initialArgument) { 
return Async.chain().go(initialArgument); 
}