Chaining multiple ajax calls in jQuery is a powerful technique that allows you

Question

Chaining multiple ajax calls in jQuery is a powerful technique that allows you

I am looking to execute a series of N ajax requests without causing the browser to freeze, and I intend to utilize the jquery deferred object for this purpose.

Below is a sample scenario involving three requests, but in reality, my program might need to handle over 100 requests (not an exact use case, but it's crucial to ensure the success of each step before moving on to the next one):

$(document).ready(function(){

    var deferred = $.Deferred();

    var countries = ["US", "CA", "MX"];

    $.each(countries, function(index, country){

        deferred.pipe(getData(country));

    });

 });

function getData(country){

    var data = {
        "country": country  
    };


    console.log("Initiating request for [" + country + "]");

    return $.ajax({
        type: "POST",
        url: "ajax.jsp",
        data: data,
        dataType: "JSON",
        success: function(){
            console.log("Request successful for [" + country + "]");
        }
    });

}

The console log output shows that all requests are sent in parallel, with response times correlating directly to the data size for each country:

Initiating request for [US]
Initiating request for [CA]
Initiating request for [MX]
Request successful for [MX]
Request successful for [CA]
Request successful for [US]

Is there a way to queue these requests using the deferred object? I've attempted switching done to pipe but achieved the same outcome.

Desired output format:

Initiating request for [US]
Request successful for [US]
Initiating request for [CA]
Request successful for [CA]
Initiating request for [MX]
Request successful for [MX]

Edit:

While I acknowledge the suggestion to utilize an array to store request parameters, I am keen on exploring the full potential of the jquery deferred object's ability to queue requests.

My goal can be summarized as follows:

when(request[0]).pipe(request[1]).pipe(request[2])... pipe(request[N]);

However, I prefer assigning requests into the pipe one at a time to make effective use of the each traversal method:

deferred.pipe(request[0]);
deferred.pipe(request[1]);
deferred.pipe(request[2]);

jquery ajax jquery-deferred deferred

Answer 1

Answer №1

Utilizing a custom object

function DeferredAjaxHandler(options) {
    this.options = options;
    this.deferred = $.Deferred();
    this.country = options.country;
}

DeferredAjaxHandler.prototype.invokeRequest = function() {
    var self = this;
    var requestData = { country: self.country };
  
    console.log("Initiating request for [" + self.country + "]");
  
    return $.ajax({
        type: "GET",
        url: "wait.php",
        data: requestData,
        dataType: "JSON",
        success: function(){
            console.log("Successful request for [" + self.country + "]");
            self.deferred.resolve();
        }
    });
};

DeferredAjaxHandler.prototype.getPromise = function() {
    return this.deferred.promise();
};


var countriesList = ["US", "CA", "MX"];
var initialPoint = $.Deferred();
initialPoint.resolve();

$.each(countriesList, function(index, country) {
    var ajaxHandler = new DeferredAjaxHandler({ country: country });
    
    $.when(initialPoint).then(function() {
        ajaxHandler.invokeRequest();
    });
    
    initialPoint = ajaxHandler;
});

Fiddle http://jsfiddle.net/5mZ3P/1/

To clarify further, the final lines can be rewritten as follows:

d1 = new DeferredAjaxHandler( {country:"US"} );
d2 = new DeferredAjaxHandler( {country:"CA"} );
d3 = new DeferredAjaxHandler( {country:"MX"} );

$.when( d1 ).then( function() { d2.invokeRequest(); } );
$.when( d2 ).then( function() { d3.invokeRequest(); } );

Using pipes

function sendHttpRequestToServer(country) {
        return $.ajax({
            type: "GET",
            url: "wait.php",
            data: {country: country},
            dataType: "JSON",
            success: function(){
                console.log("Successful request for [" + country + "]");
            }
        });
}

var allCountries = ["US", "CA", "MX"];
var startingDeferred = $.Deferred();
startingDeferred.resolve();

$.each(allCountries, function(idx, currentCountry) {
    startingDeferred = startingDeferred.pipe( function() {
        console.log("Making request for [" + currentCountry + "]");
        return sendHttpRequestToServer(currentCountry);
    });
});

http://jsfiddle.net/oW8zb/1/

Update: A fiddle displaying the log in the result panel http://jsfiddle.net/oW8zb/3/

Each pipe call generates a fresh promise that is subsequently used for the next pipe. It should be noted that only the success function is provided here, and a similar function should handle failures.

In both solutions, the Ajax requests are postponed until they are required by encapsulating them in a function, and a new promise is established for each element in the list to construct the chain.

I find that using the custom object offers a more straightforward way to manipulate the chain, whereas the pipes approach might be more preferable depending on your preferences.

Important Note: commencing from jQuery 1.8, deferred.pipe() has been deprecated; deferred.then is its replacement.

Answer 2

Utilizing a custom object

function DeferredAjaxHandler(options) {
    this.options = options;
    this.deferred = $.Deferred();
    this.country = options.country;
}

DeferredAjaxHandler.prototype.invokeRequest = function() {
    var self = this;
    var requestData = { country: self.country };
  
    console.log("Initiating request for [" + self.country + "]");
  
    return $.ajax({
        type: "GET",
        url: "wait.php",
        data: requestData,
        dataType: "JSON",
        success: function(){
            console.log("Successful request for [" + self.country + "]");
            self.deferred.resolve();
        }
    });
};

DeferredAjaxHandler.prototype.getPromise = function() {
    return this.deferred.promise();
};


var countriesList = ["US", "CA", "MX"];
var initialPoint = $.Deferred();
initialPoint.resolve();

$.each(countriesList, function(index, country) {
    var ajaxHandler = new DeferredAjaxHandler({ country: country });
    
    $.when(initialPoint).then(function() {
        ajaxHandler.invokeRequest();
    });
    
    initialPoint = ajaxHandler;
});

Fiddle http://jsfiddle.net/5mZ3P/1/

To clarify further, the final lines can be rewritten as follows:

d1 = new DeferredAjaxHandler( {country:"US"} );
d2 = new DeferredAjaxHandler( {country:"CA"} );
d3 = new DeferredAjaxHandler( {country:"MX"} );

$.when( d1 ).then( function() { d2.invokeRequest(); } );
$.when( d2 ).then( function() { d3.invokeRequest(); } );

Using pipes

function sendHttpRequestToServer(country) {
        return $.ajax({
            type: "GET",
            url: "wait.php",
            data: {country: country},
            dataType: "JSON",
            success: function(){
                console.log("Successful request for [" + country + "]");
            }
        });
}

var allCountries = ["US", "CA", "MX"];
var startingDeferred = $.Deferred();
startingDeferred.resolve();

$.each(allCountries, function(idx, currentCountry) {
    startingDeferred = startingDeferred.pipe( function() {
        console.log("Making request for [" + currentCountry + "]");
        return sendHttpRequestToServer(currentCountry);
    });
});

http://jsfiddle.net/oW8zb/1/

Update: A fiddle displaying the log in the result panel http://jsfiddle.net/oW8zb/3/

Each pipe call generates a fresh promise that is subsequently used for the next pipe. It should be noted that only the success function is provided here, and a similar function should handle failures.

In both solutions, the Ajax requests are postponed until they are required by encapsulating them in a function, and a new promise is established for each element in the list to construct the chain.

I find that using the custom object offers a more straightforward way to manipulate the chain, whereas the pipes approach might be more preferable depending on your preferences.

Important Note: commencing from jQuery 1.8, deferred.pipe() has been deprecated; deferred.then is its replacement.

Answer 3

Answer №2

Note: With the release of jquery 1.8, you now have the option to use .then in place of .pipe. The .then function will return a new promise while .pipe has been deprecated as it is no longer necessary. For more information on promises, refer to the promises spec, and for a cleaner library of javascript promises without dependency on jquery, check out q.js.

countries.reduce(function(l, r){
  return l.then(function(){return getData(r)});
}, $.Deferred().resolve());

If you prefer using q.js:

//create a closure for each call
function getCountry(c){return function(){return getData(c)};}
//fire the closures one by one
//note: in Q, when(p1,f1) is the static version of p1.then(f1)
countries.map(getCountry).reduce(Q.when, Q());

Original response:

Here's another pipeline method; not for the faint-hearted, but a bit more concise:

countries.reduce(function(l, r){
  return l.pipe(function(){return getData(r)});
}, $.Deferred().resolve());

Refer to the Reduce documentation for a better understanding of how the code above functions. Essentially, it takes two arguments - a callback and an initial value.

The callback is applied iteratively to all elements of the array, where the result of the previous iteration is passed as the first argument, and the current element as the second argument. The key here is that the getData() function returns a jquery deferred promise, and the pipe ensures that before calling getData on the current element, the getData from the previous element is completed.

The second argument $.Deferred().resolve() represents a resolved deferred value. It is supplied to the first execution of the callback, ensuring that the getData for the first element is called immediately.

Answer 4

Note: With the release of jquery 1.8, you now have the option to use .then in place of .pipe. The .then function will return a new promise while .pipe has been deprecated as it is no longer necessary. For more information on promises, refer to the promises spec, and for a cleaner library of javascript promises without dependency on jquery, check out q.js.

countries.reduce(function(l, r){
  return l.then(function(){return getData(r)});
}, $.Deferred().resolve());

If you prefer using q.js:

//create a closure for each call
function getCountry(c){return function(){return getData(c)};}
//fire the closures one by one
//note: in Q, when(p1,f1) is the static version of p1.then(f1)
countries.map(getCountry).reduce(Q.when, Q());

Original response:

Here's another pipeline method; not for the faint-hearted, but a bit more concise:

countries.reduce(function(l, r){
  return l.pipe(function(){return getData(r)});
}, $.Deferred().resolve());

Refer to the Reduce documentation for a better understanding of how the code above functions. Essentially, it takes two arguments - a callback and an initial value.

The callback is applied iteratively to all elements of the array, where the result of the previous iteration is passed as the first argument, and the current element as the second argument. The key here is that the getData() function returns a jquery deferred promise, and the pipe ensures that before calling getData on the current element, the getData from the previous element is completed.

The second argument $.Deferred().resolve() represents a resolved deferred value. It is supplied to the first execution of the callback, ensuring that the getData for the first element is called immediately.

Answer 5

Answer №3

I can see why you might consider doing this, but it's important to keep track of all the URLs that need to be requested. Only move on to the next one once your success function has been triggered. In other words, success will determine if more calls to deferred should be made.

Answer 6

I can see why you might consider doing this, but it's important to keep track of all the URLs that need to be requested. Only move on to the next one once your success function has been triggered. In other words, success will determine if more calls to deferred should be made.

Answer 7

Answer №4

My experience with using jQuery queues has been quite successful.

$(function(){
    $.each(countries, function(i,country){
      $('body').queue(function() {
        getData(country);
      });
    });
});

var getData = function(country){
  $.ajax({
    url : 'ajax.jsp',
    data : { country : country },
    type : 'post',
    success : function() {                          
      // Proceed to the next ajax call
      $('body').dequeue();
    },
    error : function(){
      // Clear all queued ajax calls in case of an error
      $('body').clearQueue();
    }
  });
};

Answer 8

My experience with using jQuery queues has been quite successful.

$(function(){
    $.each(countries, function(i,country){
      $('body').queue(function() {
        getData(country);
      });
    });
});

var getData = function(country){
  $.ajax({
    url : 'ajax.jsp',
    data : { country : country },
    type : 'post',
    success : function() {                          
      // Proceed to the next ajax call
      $('body').dequeue();
    },
    error : function(){
      // Clear all queued ajax calls in case of an error
      $('body').clearQueue();
    }
  });
};

Answer 9

Answer №5

While I might be a bit late to the party, there are some potential issues with your original code that could cause problems.

The getData(country) function is being called immediately due to how you structured your pipe's parameter. As it stands, getData() is executed right away and its result (the ajax promise) is passed as an object rather than a callback function to pipe(). This causes the pipe to resolve immediately.

To address this, consider making it:

deferred.pipe(function () { return getData(country); });

By using a callback function instead, you ensure that the getData() functions only execute once the parent deferred has resolved. However, chaining all your pipes to the master deferred may result in them running somewhat concurrently, so it's worth considering restructuring.

You could try something along these lines:

var countries = ["US", "CA", "MX"];
var deferred = $.Deferred();
var promise = deferred.promise();

$.each(countries, function(index, country) {
    promise = promise.pipe(function () { return getData(country); });
});

deferred.resolve();

Answer 10

While I might be a bit late to the party, there are some potential issues with your original code that could cause problems.

The getData(country) function is being called immediately due to how you structured your pipe's parameter. As it stands, getData() is executed right away and its result (the ajax promise) is passed as an object rather than a callback function to pipe(). This causes the pipe to resolve immediately.

To address this, consider making it:

deferred.pipe(function () { return getData(country); });

By using a callback function instead, you ensure that the getData() functions only execute once the parent deferred has resolved. However, chaining all your pipes to the master deferred may result in them running somewhat concurrently, so it's worth considering restructuring.

You could try something along these lines:

var countries = ["US", "CA", "MX"];
var deferred = $.Deferred();
var promise = deferred.promise();

$.each(countries, function(index, country) {
    promise = promise.pipe(function () { return getData(country); });
});

deferred.resolve();

Answer 11

Answer №6

Important Update: The use of deferred.pipe is now considered outdated

Although there is a significant amount of code provided here, it is essential to note that the functionality is already well-documented in the jQuery API. For detailed information, please refer to http://api.jquery.com/deferred.pipe/

You have the option to continuously pipe them until reaching the completion of all 100 required tasks.

An alternative solution involves creating N calls and consolidating all their data into a single function. Please keep in mind that this method returns the data rather than the entire XHR object. Further details can be found at https://gist.github.com/1219564

Answer 12

Important Update: The use of deferred.pipe is now considered outdated

Although there is a significant amount of code provided here, it is essential to note that the functionality is already well-documented in the jQuery API. For detailed information, please refer to http://api.jquery.com/deferred.pipe/

You have the option to continuously pipe them until reaching the completion of all 100 required tasks.

An alternative solution involves creating N calls and consolidating all their data into a single function. Please keep in mind that this method returns the data rather than the entire XHR object. Further details can be found at https://gist.github.com/1219564

Chaining multiple ajax calls in jQuery is a powerful technique that allows you

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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