jQuery 1.5 添加了“延迟对象”。它们是什么，它们究竟是做什么的？
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101
Deferred Object
As of jQuery 1.5, the Deferred object provides a way to register multiple callbacks into self-managed callback queues, invoke callback queues as appropriate, and relay the success or failure state of any synchronous or asynchronous function.
Deferred Methods:
- deferred.done()
- Add handlers to be called when the Deferred object is resolved.
- deferred.fail()
- Add handlers to be called when the Deferred object is rejected.
- deferred.isRejected()
- Determine whether a Deferred object has been rejected.
- deferred.isResolved()
- Determine whether a Deferred object has been resolved.
- deferred.reject()
- Reject a Deferred object and call any failCallbacks with the given args.
- deferred.rejectWith()
- Reject a Deferred object and call any failCallbacks with the given context and args.
- deferred.resolve()
- Resolve a Deferred object and call any doneCallbacks with the given args.
- deferred.resolveWith()
- Resolve a Deferred object and call any doneCallbacks with the given context and args.
- deferred.then()
- Add handlers to be called when the Deferred object is resolved or rejected.
Deferred In Action:
$.get("test.php").done(
function(){ alert("$.get succeeded"); }
);
$.get("test.php")
.done(function(){ alert("$.get succeeded"); })
.fail(function(){ alert("$.get failed!"); });
And it seems that the existing ajax() method callbacks can be chained rather than declared in the settings:
var jqxhr = $.ajax({ url: "example.php" })
.success(function() { alert("success"); })
.error(function() { alert("error"); })
.complete(function() { alert("complete"); });
Working Example From Eric Hynds blog post: http://jsfiddle.net/ehynds/Mrqf8/
jqXHR
As of jQuery 1.5, the $.ajax() method returns the jXHR object, which is a superset of the XMLHTTPRequest object. For more information, see thejXHR section of the $.ajax entry
From JQUERY 1.5 RELEASED:
DEFERRED OBJECTS
Along with the rewrite of the Ajax module a new feature was introduced which was also made publicly available: Deferred Objects. This API allows you to work with return values that may not be immediately present (such as the return result from an asynchronous Ajax request). Additionally it gives you the ability to attach multiple event handlers (something that wasn’t previously possible in the Ajax API).
Additionally you can make your own deferred objects using the exposed jQuery.Deferred. More information about this API can be found in the Deferred Object documentation.
Eric Hynds has written up a good tutorial on Using Deferreds in jQuery 1.5.
于 2011-02-01T18:55:47.833 回答
13
与其告诉你它做了什么，我会告诉你它做了什么并解释它。
jQuery 1.5 相关源代码的副本，其中包含注释说明它在做什么。我认为评论大多是正确的。
这可能是有益的
// promiseMethods. These are the methods you get when you ask for a promise.
// A promise is a "read-only" version
// fullMethods = "then done fail resolve resolveWith reject rejectWith isResolve isRejected promise cancel".split(" ")
// As you can see it removes resolve/reject so you can't actaully trigger a
// anything on the deferred object, only process callbacks when it "finishes".
promiseMethods = "then done fail isResolved isRejected promise".split(" "),
// Create a simple deferred (one callbacks list)
/* Class: _Deferred.
* methods: done, resolve, resolveWith, isResolved
* internal method: cancel
*
* Basically allows you to attach callbacks with the done method.
* Then resolve the deferred action whenever you want with an argument.
* All the callbacks added with done will be called with the resolved argument
* Any callbacks attached after resolvement will fire immediatly.
*
* resolveWith allows you to set the this scope in the callbacks fired.
*
* isResolved just checks whether it's resolved yet.
*
* cancel blocks resolve/resolveWith from firing. the methods added throug
* done will never be called
*/
_Deferred: function () {
var // callbacks list
callbacks = [],
// stored [ context , args ]
// stores the context & args that .resolve was called with
fired,
// to avoid firing when already doing so
firing,
// flag to know if the deferred has been cancelled
// in Deferred cancel gets called after the first resolve call
cancelled,
// the deferred itself
deferred = {
// done( f1, f2, ...)
done: function () {
if (!cancelled) {
var args = arguments,
i, length,
// elem in callback list
elem,
// type of elem in callback list
type,
// cached context & args for when done is called
// after resolve has been
_fired;
// If resolve has been called already
if (fired) {
// mark it locally
_fired = fired;
// set fired to 0. This is neccesary to handle
// how done deals with arrays recursively
// only the original .done call handles fired
// any that unwrap arrays and call recursively
// dont handle the fired.
fired = 0;
}
// for each function append it to the callback list
for (i = 0, length = args.length; i < length; i++) {
elem = args[i];
type = jQuery.type(elem);
// if argument is an array then call done recursively
// effectively unwraps the array
if (type === "array") {
// def.done([f1, f2, f3]) goes to
// def.done(f1, f2, f3) through the apply
deferred.done.apply(deferred, elem);
} else if (type === "function") {
// if its a function add it to the callbacks
callbacks.push(elem);
}
}
// if it's already been resolved then call resolveWith using
// the cahced context and arguments to call the callbacks
// immediatly
if (_fired) {
deferred.resolveWith(_fired[0], _fired[1]);
}
}
return this;
},
// resolve with given context and args
resolveWith: function (context, args) {
// if its been cancelled then we can't resolve
// if it has fired then we can't fire again
// if it's currently firing then we can't fire. This check is
// there because of the try finally block. It ensures we
// cant call resolve between the try & finally in the catch phase.
if (!cancelled && !fired && !firing) {
firing = 1;
// try block because your calling external callbacks
// made by the user which are not bugfree.
// the finally block will always run no matter how bad
// the internal code is.
try {
while (callbacks[0]) {
callbacks.shift().apply(context, args);
}
// cache the content and arguments taht have been called
// and set firing to false.
} finally {
fired = [context, args];
firing = 0;
}
}
return this;
},
// resolve with this as context and given arguments
// just maps to resolveWith, this sets the this scope as normal
// maps to this.promise which is the read only version of Deferred.
resolve: function () {
deferred.resolveWith(jQuery.isFunction(this.promise) ? this.promise() :
this, arguments);
return this;
},
// Has this deferred been resolved?
// checks whether it's firing or if it has fired.
isResolved: function () {
return !!(firing || fired);
},
// Cancels the action. To be used internally
cancel: function () {
cancelled = 1;
callbacks = [];
return this;
}
};
return deferred;
},
/* Class: Deferred.
* methods: then, done, fail, resolve, reject, resolveWith, rejectWith, isResolved,
isRejected, promise
*
* then is a shortcut for both assigning done & fail in one function.
*
* This one has two underlying lists with different semantic meanings. You
* can bind to both the done callbacks and the fail callbacks then either
* resolve or reject your Deferred object.
*
* You can check whether it has been resolved or rejected. useful to see
* Afterwards which one has happened.
*
* Call .promise to return a new object which doesn't have the resolve/reject
* methods on it. This means you can only bind to it and not resolve/reject it.
* This is effectively read-only.
*
*/
// Full fledged deferred (two callbacks list)
Deferred: function (func) {
// the main deferred which deals with the success callbacks
var deferred = jQuery._Deferred(),
// the failure deferred which deals with the rejected callbacks
failDeferred = jQuery._Deferred(),
// the read only promise is cached.
promise;
// Add errorDeferred methods, then and promise
jQuery.extend(deferred, {
// def.then([f1, f2, ...], [g1, g2, ...] is a short hand for
// def.done([f1, f2, ...])
// def.fail([g1, g2, ...])
then: function (doneCallbacks, failCallbacks) {
// fail exists here because this code will only run after
// deferred has been extended.
deferred.done(doneCallbacks).fail(failCallbacks);
return this;
},
// map def.fail to the second underlying deferred callback list
// map all the other methods for rejection/failure to the underlying
// failDeffered object so that Deferred has two callback lists stored
// internally.
fail: failDeferred.done,
rejectWith: failDeferred.resolveWith,
reject: failDeferred.resolve,
isRejected: failDeferred.isResolved,
// Get a promise for this deferred
// If obj is provided, the promise aspect is added to the object
// no clue what to do with "i"
promise: function (obj, i /* internal */ ) {
// if no argument is passed then just extend promise
if (obj == null) {
// if cached return the cache.
if (promise) {
return promise;
}
// set promise & arg to be {}
promise = obj = {};
}
// for each promiseMethods in the read only promise list
i = promiseMethods.length;
while (i--) {
// set the deferred method on the object
obj[promiseMethods[i]] = deferred[promiseMethods[i]];
}
// returns the "read-only" deferred without
// resolve, resolveWith, reject & rejectWith.
// So you cant "resolve" it but only add "done" functions
return obj;
}
});
// Make sure only one callback list will be used
// if either resolve or reject is called cancel both.
// this means that the one that has been called cant be called again
// and the other one will never be called. So only the done or the fail
// methods will ever be called
deferred.then(failDeferred.cancel, deferred.cancel);
// Don't mess with cancel!
// Unexpose cancel
delete deferred.cancel;
// Call given func if any
// function argument to be called. This was passed in. Allows you to
// handle the deferred object after creating a new one, both as this scope
// and as a new argument.
if (func) {
func.call(deferred, deferred);
}
return deferred;
},
/* Method: when
* Arguments: none OR 1 of type(any & !deferred) OR n of type(deferred).
*
* If no arguments are passed then it gets resolved immediatly. A good way to
* call multiple callback functions? Don't really know a good use of $.when()
*
* If one argument is passed and its not a deferred object then it resolves
* immediatly and passes that argument to all the done callbacks attached.
*
* if n arguments are passed of type deferred object then the the done callbacks
* will only fire if all of them succeed. If a single one fails then the
* fail callbacks fire.
*
* Returns a promise read-only deferred object
*/
// Deferred helper
when: function (object) {
var args = arguments,
length = args.length,
// If you pass in a deferred object then set deferred to be the promise
// if you pass in anything else then set deferred to be a new deferred
deferred = length <= 1 && object && jQuery.isFunction(object.promise) ?
object :
jQuery.Deferred(),
// cache the promise
promise = deferred.promise(),
// store an array
resolveArray;
// if multiple objects are passed in
if (length > 1) {
// create an arrey to store of values.
resolveArray = new Array(length);
// for each object that we wait on
jQuery.each(args, function (index, element) {
// when that object resolves then
jQuery.when(element).then(function (value) {
// store value in the array or store an array of values in it
resolveArray[index] = arguments.length > 1 ? slice.call(arguments, 0) :
value;
// if length === 1 then we finished calling them all
if (!--length) {
// resolve the deferred object with the read only promise
// as context and the resolved values array as the argument
deferred.resolveWith(promise, resolveArray);
}
// if any fail then we reject or deferred
}, deferred.reject);
});
// if deferred was newly created but there was only one argument then
// resolve it immediatly with the argument.
} else if (deferred !== object) {
deferred.resolve(object);
}
// return the read-only deferred.
return promise;
},
于 2011-02-01T21:04:59.193 回答
9
如果我错了，请纠正我，但它最近让我觉得它本质上是一个异步任务运行器。承诺是一个结果合同，确保你收到……一些东西，但不保证你什么时候能得到它。
于 2011-09-06T23:57:28.630 回答
3
在使用 Javascript 工作时，我们会遇到函数调用是异步的情况。那就是 calee 函数（假设 X）的流程不会等待被调用的异步函数（假设 Y）。典型的例子是当我们调用服务器从数据库或 HTML 页面中获取一些数据时。如果这些调用不是异步的，用户界面将被卡住等待服务器响应。当您想按顺序执行事物时，这种异步性质会导致问题，例如，您想在 Y（异步）完成执行或完成获取数据后打印某些内容。这里 jQuery 为我们提供了延迟对象。基本上，jQuery 已经处理了我们通常为解决这种情况而编写的所有样板代码。这是一个简单的例子：
$.ajax({
...
}).done(function(){
//write here what you wish to do when this ajax call is success
}).fail(function(){
//write here what you wish to do on failure of this ajax call
}); //see more on jQuery Deferred page
您可以编写自己的延迟（异步）函数
function DoSomethingTimeConsumingAsynch(){
var deferred = $.Deferred();
_.defer(function(){ //I am using underscore, you can also use setTimeout
...
deferred.resolve();//When the process is done successfully
...
deferred.reject(); //When the process has failed
});
return deferred;
}
//HEre how to use your own asynch function
DoSomethingTimeConsumingAsynch()
.done(function(){
//this will be invoked on success
})
.fail(function(){
//this will be invoked on failure
})
我希望这会有所帮助。
于 2016-01-26T10:13:56.440 回答