Que sont les objets différés?
jQuery 1.5 ajoute "Objets différés". Que sont-ils et que font-ils exactement?
Objet différé
À partir de jQuery 1.5, l'objet Deferred fournit un moyen d'enregistrer plusieurs rappels dans des files d'attente de rappel autogérées, d'appeler des files d'attente de rappel selon le cas et de relayer l'état de réussite ou d'échec de toute fonction synchrone ou asynchrone.
Méthodes différées:
- deferred.done ()
- Ajoutez des gestionnaires à appeler lorsque l'objet différé est résolu.
- deferred.fail ()
- Ajoutez des gestionnaires à appeler lorsque l'objet différé est rejeté.
- deferred.isRejected ()
- Déterminez si un objet différé a été rejeté.
- deferred.isResolved ()
- Déterminez si un objet différé a été résolu.
- deferred.reject ()
- Rejetez un objet différé et appelez tous les failCallbacks avec les arguments donnés.
- deferred.rejectWith ()
- Rejetez un objet différé et appelez tous les failCallbacks avec le contexte et les arguments donnés.
- deferred.resolve ()
- Résolvez un objet différé et appelez tous doneCallbacks avec les arguments donnés.
- deferred.resolveWith ()
- Résolvez un objet différé et appelez tous doneCallbacks avec le contexte et les arguments donnés.
- deferred.then ()
- Ajoutez des gestionnaires à appeler lorsque l'objet différé est résolu ou rejeté.
différé dans l'action:
$.get("test.php").done(
function(){ alert("$.get succeeded"); }
);
$.get("test.php")
.done(function(){ alert("$.get succeeded"); })
.fail(function(){ alert("$.get failed!"); });
Et il semble que les rappels de méthode ajax () existants puissent être chaînés plutôt que déclarés dans les paramètres:
var jqxhr = $.ajax({ url: "example.php" })
.success(function() { alert("success"); })
.error(function() { alert("error"); })
.complete(function() { alert("complete"); });
Exemple de travail extrait du blog d'Eric Hynds : http://jsfiddle.net/ehynds/Mrqf8/
jqXHR
Depuis jQuery 1.5, la méthode $ .ajax () renvoie l'objet jXHR, qui est un sur-ensemble de l'objet XMLHTTPRequest. Pour plus d'informations, voir la section jXHR de l'entrée $ .ajax.
De JQUERY 1.5 RELEASED :
OBJETS DIFFÉRÉS
Parallèlement à la réécriture du module Ajax, une nouvelle fonctionnalité a été introduite, qui a également été rendue publique: Objets différés . Cette API vous permet de travailler avec des valeurs de retour qui peuvent ne pas être immédiatement présentes (telles que le résultat de retour d'une requête Ajax asynchrone). De plus, il vous permet d’attacher plusieurs gestionnaires d’événements (ce qui n’était pas possible auparavant dans l’API Ajax).
De plus, vous pouvez créer vos propres objets différés à l’aide de jQuery.Deferred exposé. Pour plus d'informations sur cette API, reportez-vous à la documentation objet différé .
Eric Hynds a rédigé un bon tutoriel sur tilisation de différés dans jQuery 1.5 .
Plutôt que de vous dire ce que ça fait, je vais vous montrer ce que ça fait et vous l'expliquer.
Une copie de la source associée de jQuery 1.5 avec une annotation expliquant ce qu’elle fait. Je pense que les commentaires sont pour la plupart corrects.
Cela peut être bénéfique
// 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;
},
Corrigez-moi si je me trompe, mais on m'a récemment dit qu'il s'agissait essentiellement d'un gestionnaire de tâches asynchrone. La promesse est un contrat de résultat, vous assurant de recevoir… quelque chose, mais sans garantie de l'obtenir.
En travaillant en Javascript, nous rencontrons des situations où les appels de fonctions sont asynchrones. C'est-à-dire que le flux de la fonction calee (disons X) n'attend pas la fonction asynchrone appelée (disons Y). Un exemple typique est lorsque nous appelons un serveur pour récupérer des données d’une base de données ou d’une page HTML. Si ces appels n'étaient pas asynchrones, l'interface utilisateur sera bloquée dans l'attente de la réponse du serveur. Cette nature asynchrone pose un problème lorsque vous souhaitez exécuter des tâches dans un ordre, par exemple, vous souhaitez imprimer quelque chose après l'exécution de Y (asynch) ou de l'extraction de données. Ici, jQuery nous fournit un objet modifié. En gros, jQuery s’est occupé de tout le code standard que nous écrivons habituellement pour résoudre cette situation. Voici un exemple simple:
$.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
Vous pouvez écrire votre propre fonction différée (asynchrone)
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
})
J'espère que cela a aidé.