Most votes on ajax questions 1

Most votes on ajax questions 1. #1 How do I return the response from an asynchronous call? #2 Why does Google prepend while(1); to their JSON responses? #3 How can I upload files asynchronously? #4 How do I format a Microsoft JSON date? #5 Abort Ajax requests using jQuery #6 Disable same origin policy in Chrome #7 How to manage a redirect request after a jQuery Ajax call #8 How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request? #9 How to manually send HTTP POST requests from Firefox or Chrome browser? #10 Serializing to JSON in jQuery

Read all the top votes questions and answers in a single page.

#1: How do I return the response from an asynchronous call? (Score: 5928)

Created: 2013-01-08 Last updated: 2020-09-11

Tags: javascript, jquery, ajax, asynchronous

I have a function foo which makes an asynchronous request. How can I return the response/result from foo?

I tried returning the value from the callback, as well as assigning the result to a local variable inside the function and returning that one, but none of those ways actually return the response (they all return undefined or whatever the initial value of the variable result is).

Example using jQuery’s ajax function:

function foo() {
    var result;

        url: '...',
        success: function(response) {
            result = response;
            // return response; // <- I tried that one as well

    return result; // It always returns `undefined`

Example using node.js:

function foo() {
    var result;

    fs.readFile("path/to/file", function(err, data) {
        result = data;
        // return data; // <- I tried that one as well

    return result; // It always returns `undefined`

Example using the then block of a promise:

function foo() {
    var result;

    fetch(url).then(function(response) {
        result = response;
        // return response; // <- I tried that one as well

    return result; // It always returns `undefined`

#1 Best answer 1 of How do I return the response from an asynchronous call? (Score: 6034)

Created: 2013-01-08 Last updated: 2021-04-09

→ For a more general explanation of async behaviour with different examples, please see

→ If you already understand the problem, skip to the possible solutions below.

The problem

The A in Ajax stands for asynchronous. That means sending the request (or rather receiving the response) is taken out of the normal execution flow. In your example, $.ajax returns immediately and the next statement, return result;, is executed before the function you passed as success callback was even called.

Here is an analogy which hopefully makes the difference between synchronous and asynchronous flow clearer:


Imagine you make a phone call to a friend and ask him to look something up for you. Although it might take a while, you wait on the phone and stare into space, until your friend gives you the answer that you needed.

The same is happening when you make a function call containing “normal” code:

function findItem() {
    var item;
    while(item_not_found) {
        // search
    return item;

var item = findItem();

// Do something with item

Even though findItem might take a long time to execute, any code coming after var item = findItem(); has to wait until the function returns the result.


You call your friend again for the same reason. But this time you tell him that you are in a hurry and he should call you back on your mobile phone. You hang up, leave the house, and do whatever you planned to do. Once your friend calls you back, you are dealing with the information he gave to you.

That’s exactly what’s happening when you do an Ajax request.

findItem(function(item) {
    // Do something with the item

Instead of waiting for the response, the execution continues immediately and the statement after the Ajax call is executed. To get the response eventually, you provide a function to be called once the response was received, a callback (notice something? call back ?). Any statement coming after that call is executed before the callback is called.


Embrace the asynchronous nature of JavaScript! While certain asynchronous operations provide synchronous counterparts (so does “Ajax”), it’s generally discouraged to use them, especially in a browser context.

Why is it bad do you ask?

JavaScript runs in the UI thread of the browser and any long-running process will lock the UI, making it unresponsive. Additionally, there is an upper limit on the execution time for JavaScript and the browser will ask the user whether to continue the execution or not.

All of this is a really bad user experience. The user won’t be able to tell whether everything is working fine or not. Furthermore, the effect will be worse for users with a slow connection.

In the following we will look at three different solutions that are all building on top of each other:

  • Promises with async/await (ES2017+, available in older browsers if you use a transpiler or regenerator)
  • Callbacks (popular in node)
  • Promises with then() (ES2015+, available in older browsers if you use one of the many promise libraries)

All three are available in current browsers, and node 7+.

ES2017+: Promises with async/await

The ECMAScript version released in 2017 introduced syntax-level support for asynchronous functions. With the help of async and await, you can write asynchronous in a “synchronous style”. The code is still asynchronous, but it’s easier to read/understand.

async/await builds on top of promises: an async function always returns a promise. await “unwraps” a promise and either result in the value the promise was resolved with or throws an error if the promise was rejected.

Important: You can only use await inside an async function. Right now, top-level await isn’t yet supported, so you might have to make an async IIFE (Immediately Invoked Function Expression) to start an async context.

You can read more about async and await on MDN.

Here is an example that builds on top of delay above:

// Using 'superagent' which will return a promise.
var superagent = require('superagent')

// This is isn't declared as `async` because it already returns a promise
function delay() {
  // `delay` returns a promise
  return new Promise(function(resolve, reject) {
    // Only `delay` is able to resolve or reject the promise
    setTimeout(function() {
      resolve(42); // After 3 seconds, resolve the promise with value 42
    }, 3000);

async function getAllBooks() {
  try {
    // GET a list of book IDs of the current user
    var bookIDs = await superagent.get('/user/books');
    // wait for 3 seconds (just for the sake of this example)
    await delay();
    // GET information about each book
    return await superagent.get('/books/ids='+JSON.stringify(bookIDs));
  } catch(error) {
    // If any of the awaited promises was rejected, this catch block
    // would catch the rejection reason
    return null;

// Start an IIFE to use `await` at the top level
(async function(){
  let books = await getAllBooks();

Current browser and node versions support async/await. You can also support older environments by transforming your code to ES5 with the help of regenerator (or tools that use regenerator, such as Babel).

Let functions accept callbacks

A callback is when function 1 is passed to function 2. Function 2 can call function 1 whenever it is ready. In the context of an asynchronous process, the callback will be called whenever the asynchronous process is done. Usually, the result is passed to the callback.

In the example of the question, you can make foo accept a callback and use it as success callback. So this

var result = foo();
// Code that depends on 'result'


foo(function(result) {
    // Code that depends on 'result'

Here we defined the function “inline” but you can pass any function reference:

function myCallback(result) {
    // Code that depends on 'result'


foo itself is defined as follows:

function foo(callback) {
        // ...
        success: callback

callback will refer to the function we pass to foo when we call it and we pass it on to success. I.e. once the Ajax request is successful, $.ajax will call callback and pass the response to the callback (which can be referred to with result, since this is how we defined the callback).

You can also process the response before passing it to the callback:

function foo(callback) {
        // ...
        success: function(response) {
            // For example, filter the response

It’s easier to write code using callbacks than it may seem. After all, JavaScript in the browser is heavily event-driven (DOM events). Receiving the Ajax response is nothing else but an event. Difficulties could arise when you have to work with third-party code, but most problems can be solved by just thinking through the application flow.

ES2015+: Promises with then()

The Promise API is a new feature of ECMAScript 6 (ES2015), but it has good browser support already. There are also many libraries which implement the standard Promises API and provide additional methods to ease the use and composition of asynchronous functions (e.g., bluebird).

Promises are containers for future values. When the promise receives the value (it is resolved) or when it is canceled (rejected), it notifies all of its “listeners” who want to access this value.

The advantage over plain callbacks is that they allow you to decouple your code and they are easier to compose.

Here is an example of using a promise:

function delay() {
  // `delay` returns a promise
  return new Promise(function(resolve, reject) {
    // Only `delay` is able to resolve or reject the promise
    setTimeout(function() {
      resolve(42); // After 3 seconds, resolve the promise with value 42
    }, 3000);

  .then(function(v) { // `delay` returns a promise
    console.log(v); // Log the value once it is resolved
  .catch(function(v) {
    // Or do something else if it is rejected
    // (it would not happen in this example, since `reject` is not called).

Applied to our Ajax call we could use promises like this:

function ajax(url) {
  return new Promise(function(resolve, reject) {
    var xhr = new XMLHttpRequest();
    xhr.onload = function() {
    xhr.onerror = reject;'GET', url);

  .then(function(result) {
    // Code depending on result
  .catch(function() {
    // An error occurred

Describing all the advantages that promise offer is beyond the scope of this answer, but if you write new code, you should seriously consider them. They provide a great abstraction and separation of your code.

More information about promises: HTML5 rocks - JavaScript Promises

Side note: jQuery’s deferred objects

Deferred objects are jQuery’s custom implementation of promises (before the Promise API was standardized). They behave almost like promises but expose a slightly different API.

Every Ajax method of jQuery already returns a “deferred object” (actually a promise of a deferred object) which you can just return from your function:

function ajax() {
    return $.ajax(...);

ajax().done(function(result) {
    // Code depending on result
}).fail(function() {
    // An error occurred

Side note: Promise gotchas

Keep in mind that promises and deferred objects are just containers for a future value, they are not the value itself. For example, suppose you had the following:

function checkPassword() {
    return $.ajax({
        url: '/password',
        data: {
            username: $('#username').val(),
            password: $('#password').val()
        type: 'POST',
        dataType: 'json'

if (checkPassword()) {
    // Tell the user they're logged in

This code misunderstands the above asynchronous issues. Specifically, $.ajax() doesn’t freeze the code while it checks the ‘/password’ page on your server - it sends a request to the server and while it waits, it immediately returns a jQuery Ajax Deferred object, not the response from the server. That means the if statement is going to always get this Deferred object, treat it as true, and proceed as though the user is logged in. Not good.

But the fix is easy:

.done(function(r) {
    if (r) {
        // Tell the user they're logged in
    } else {
        // Tell the user their password was bad
.fail(function(x) {
    // Tell the user something bad happened

As I mentioned, some(!) asynchronous operations have synchronous counterparts. I don’t advocate their use, but for completeness' sake, here is how you would perform a synchronous call:

Without jQuery

If you directly use a XMLHttpRequest object, pass false as third argument to .open.


If you use jQuery, you can set the async option to false. Note that this option is deprecated since jQuery 1.8. You can then either still use a success callback or access the responseText property of the jqXHR object:

function foo() {
    var jqXHR = $.ajax({
        async: false
    return jqXHR.responseText;

If you use any other jQuery Ajax method, such as $.get, $.getJSON, etc., you have to change it to $.ajax (since you can only pass configuration parameters to $.ajax).

Heads up! It is not possible to make a synchronous JSONP request. JSONP by its very nature is always asynchronous (one more reason to not even consider this option).

#1 Best answer 2 of How do I return the response from an asynchronous call?(Score: 1129)

Created: 2013-05-29 Last updated: 2021-04-09

If you’re not using jQuery in your code, this answer is for you

Your code should be something along the lines of this:

function foo() {
    var httpRequest = new XMLHttpRequest();'GET', "/echo/json");
    return httpRequest.responseText;

var result = foo(); // Always ends up being 'undefined'

Felix Kling did a fine job writing an answer for people using jQuery for AJAX, but I’ve decided to provide an alternative for people who aren’t.

(Note, for those using the new fetch API, Angular or promises I’ve added another answer below)

What you’re facing

This is a short summary of “Explanation of the problem” from the other answer, if you’re not sure after reading this, read that.

The A in AJAX stands for asynchronous. That means sending the request (or rather receiving the response) is taken out of the normal execution flow. In your example, .send returns immediately and the next statement, return result;, is executed before the function you passed as success callback was even called.

This means when you’re returning, the listener you’ve defined did not execute yet, which means the value you’re returning has not been defined.

Here is a simple analogy:

function getFive(){
    var a;
    return a;


The value of a returned is undefined since the a=5 part has not executed yet. AJAX acts like this, you’re returning the value before the server got the chance to tell your browser what that value is.

One possible solution to this problem is to code re-actively , telling your program what to do when the calculation completed.

function onComplete(a){ // When the code completes, do this

function getFive(whenDone){
    var a;

This is called CPS. Basically, we’re passing getFive an action to perform when it completes, we’re telling our code how to react when an event completes (like our AJAX call, or in this case the timeout).

Usage would be:


Which should alert “5” to the screen. (Fiddle).

Possible solutions

There are basically two ways how to solve this:

  1. Make the AJAX call synchronous (let’s call it SJAX).
  2. Restructure your code to work properly with callbacks.

1. Synchronous AJAX - Don’t do it!!

As for synchronous AJAX, don’t do it! Felix’s answer raises some compelling arguments about why it’s a bad idea. To sum it up, it’ll freeze the user’s browser until the server returns the response and create a very bad user experience. Here is another short summary taken from MDN on why:

XMLHttpRequest supports both synchronous and asynchronous communications. In general, however, asynchronous requests should be preferred to synchronous requests for performance reasons.

In short, synchronous requests block the execution of code… …this can cause serious issues…

If you have to do it, you can pass a flag. Here is how:

var request = new XMLHttpRequest();'GET', 'yourURL', false);  // `false` makes the request synchronous

if (request.status === 200) {// That's HTTP for 'ok'

2. Restructure code

Let your function accept a callback. In the example code foo can be made to accept a callback. We’ll be telling our code how to react when foo completes.


var result = foo();
// Code that depends on `result` goes here


foo(function(result) {
    // Code that depends on `result`

Here we passed an anonymous function, but we could just as easily pass a reference to an existing function, making it look like:

function myHandler(result) {
    // Code that depends on `result`

For more details on how this sort of callback design is done, check Felix’s answer.

Now, let’s define foo itself to act accordingly

function foo(callback) {
    var httpRequest = new XMLHttpRequest();
    httpRequest.onload = function(){ // When the request is loaded
       callback(httpRequest.responseText);// We're calling our method
    };'GET', "/echo/json");


We have now made our foo function accept an action to run when the AJAX completes successfully. We can extend this further by checking if the response status is not 200 and acting accordingly (create a fail handler and such). Effectively it is solving our issue.

If you’re still having a hard time understanding this, read the AJAX getting started guide at MDN.

See also original question in stackoverflow

#2: Why does Google prepend while(1); to their JSON responses? (Score: 4238)

Created: 2010-04-19 Last updated: 2020-01-03

Tags: javascript, json, ajax, security

Why does Google prepend while(1); to their (private) JSON responses?

For example, here’s a response while turning a calendar on and off in Google Calendar:

while (1);
  ['u', [
    ['smsSentFlag', 'false'],
    ['hideInvitations', 'false'],
    ['remindOnRespondedEventsOnly', 'true'],
    ['hideInvitations_remindOnRespondedEventsOnly', 'false_true'],
    ['Calendar ID stripped for privacy', 'false'],
    ['smsVerifiedFlag', 'true']

I would assume this is to prevent people from doing an eval() on it, but all you’d really have to do is replace the while and then you’d be set. I would assume the eval prevention is to make sure people write safe JSON parsing code.

I’ve seen this used in a couple of other places, too, but a lot more so with Google (Mail, Calendar, Contacts, etc.) Strangely enough, Google Docs starts with &&&START&&& instead, and Google Contacts seems to start with while(1); &&&START&&&.

What’s going on here?

#2 Best answer 1 of Why does Google prepend while(1); to their JSON responses? (Score: 4413)

Created: 2010-04-19 Last updated: 2019-03-10

It prevents JSON hijacking, a major JSON security issue that is formally fixed in all major browsers since 2011 with ECMAScript 5.

Contrived example: say Google has a URL like which returns the first 50 messages of your inbox in JSON format. Evil websites on other domains can’t make AJAX requests to get this data due to the same-origin policy, but they can include the URL via a <script> tag. The URL is visited with your cookies, and by overriding the global array constructor or accessor methods they can have a method called whenever an object (array or hash) attribute is set, allowing them to read the JSON content.

The while(1); or &&&BLAH&&& prevents this: an AJAX request at will have full access to the text content, and can strip it away. But a <script> tag insertion blindly executes the JavaScript without any processing, resulting in either an infinite loop or a syntax error.

This does not address the issue of cross-site request forgery.

#2 Best answer 2 of Why does Google prepend while(1); to their JSON responses?(Score: 605)

Created: 2014-02-02 Last updated: 2020-10-19

It prevents disclosure of the response through JSON hijacking.

In theory, the content of HTTP responses are protected by the Same Origin Policy: pages from one domain cannot get any pieces of information from pages on the other domain (unless explicitly allowed).

An attacker can request pages on other domains on your behalf, e.g. by using a <script src=...> or <img> tag, but it can’t get any information about the result (headers, contents).

Thus, if you visit an attacker’s page, it couldn’t read your email from

Except that when using a script tag to request JSON content, the JSON is executed as JavaScript in an attacker’s controlled environment. If the attacker can replace the Array or Object constructor or some other method used during object construction, anything in the JSON would pass through the attacker’s code, and be disclosed.

Note that this happens at the time the JSON is executed as JavaScript, not at the time it’s parsed.

There are multiple countermeasures:

Making sure the JSON never executes

By placing a while(1); statement before the JSON data, Google makes sure that the JSON data is never executed as JavaScript.

Only a legitimate page could actually get the whole content, strip the while(1);, and parse the remainder as JSON.

Things like for(;;); have been seen at Facebook for instance, with the same results.

Making sure the JSON is not valid JavaScript

Similarly, adding invalid tokens before the JSON, like &&&START&&&, makes sure that it is never executed.

Always return JSON with an Object on the outside

This is OWASP recommended way to protect from JSON hijacking and is the less intrusive one.

Similarly to the previous counter-measures, it makes sure that the JSON is never executed as JavaScript.

A valid JSON object, when not enclosed by anything, is not valid in JavaScript:

// SyntaxError: Unexpected token :

This is however valid JSON:

// Object {foo: "bar"}

So, making sure you always return an Object at the top level of the response makes sure that the JSON is not valid JavaScript, while still being valid JSON.

As noted by @hvd in the comments, the empty object {} is valid JavaScript, and knowing the object is empty may itself be valuable information.

Comparison of above methods

The OWASP way is less intrusive, as it needs no client library changes, and transfers valid JSON. It is unsure whether past or future browser bugs could defeat this, however. As noted by @oriadam, it is unclear whether data could be leaked in a parse error through an error handling or not (e.g. window.onerror).

Google’s way requires a client library in order for it to support automatic de-serialization and can be considered to be safer with regard to browser bugs.

Both methods require server side changes in order to avoid developers accidentally sending vulnerable JSON.

See also original question in stackoverflow

#3: How can I upload files asynchronously? (Score: 3018)

Created: 2008-10-03 Last updated: 2019-12-27

Tags: javascript, jquery, ajax, asynchronous, xmlhttprequest

I would like to upload a file asynchronously with jQuery.

$(document).ready(function () {
    $("#uploadbutton").click(function () {
        var filename = $("#file").val();

            type: "POST",
            url: "",
            enctype: 'multipart/form-data',
            data: {
                file: filename
            success: function () {
                alert("Data Uploaded: ");
<script src=""></script>
<input type="file" id="file" name="file" size="10"/>
<input id="uploadbutton" type="button" value="Upload"/>

Instead of the file being uploaded, I am only getting the filename. What can I do to fix this problem?

#3 Best answer 1 of How can I upload files asynchronously? (Score: 2566)

Created: 2012-01-06 Last updated: 2019-03-19

With HTML5 you can make file uploads with Ajax and jQuery. Not only that, you can do file validations (name, size, and MIME type) or handle the progress event with the HTML5 progress tag (or a div). Recently I had to make a file uploader, but I didn’t want to use Flash nor Iframes or plugins and after some research I came up with the solution.


<form enctype="multipart/form-data">
    <input name="file" type="file" />
    <input type="button" value="Upload" />

First, you can do some validation if you want. For example, in the .on('change') event of the file:

$(':file').on('change', function () {
  var file = this.files[0];

  if (file.size > 1024) {
    alert('max upload size is 1k');

  // Also see .name, .type

Now the $.ajax() submit with the button’s click:

$(':button').on('click', function () {
    // Your server script to process the upload
    url: 'upload.php',
    type: 'POST',

    // Form data
    data: new FormData($('form')[0]),

    // Tell jQuery not to process data or worry about content-type
    // You *must* include these options!
    cache: false,
    contentType: false,
    processData: false,

    // Custom XMLHttpRequest
    xhr: function () {
      var myXhr = $.ajaxSettings.xhr();
      if (myXhr.upload) {
        // For handling the progress of the upload
        myXhr.upload.addEventListener('progress', function (e) {
          if (e.lengthComputable) {
              value: e.loaded,
        }, false);
      return myXhr;

As you can see, with HTML5 (and some research) file uploading not only becomes possible but super easy. Try it with Google Chrome as some of the HTML5 components of the examples aren’t available in every browser.

#3 Best answer 2 of How can I upload files asynchronously?(Score: 289)

Created: 2008-10-03 Last updated: 2020-03-04

2019 Update: It still depends on the browsers your demographic uses.

An important thing to understand with the “new” HTML5 file API is that it wasn’t supported until IE 10. If the specific market you’re aiming at has a higher-than-average propensity toward older versions of Windows, you might not have access to it.

As of 2017, about 5% of browsers are one of IE 6, 7, 8 or 9. If you head into a big corporation (e.g., this is a B2B tool, or something you’re delivering for training) that number can skyrocket. In 2016, I dealt with a company using IE8 on over 60% of their machines.

It’s 2019 as of this edit, almost 11 years after my initial answer. IE9 and lower are globally around the 1% mark but there are still clusters of higher usage.

The important take-away from this —whatever the feature— is, check what browser your users use. If you don’t, you’ll learn a quick and painful lesson in why “works for me” isn’t good enough in a deliverable to a client. caniuse is a useful tool but note where they get their demographics from. They may not align with yours. This is never truer than enterprise environments.

My answer from 2008 follows.

However, there are viable non-JS methods of file uploads. You can create an iframe on the page (that you hide with CSS) and then target your form to post to that iframe. The main page doesn’t need to move.

It’s a “real” post so it’s not wholly interactive. If you need status you need something server-side to process that. This varies massively depending on your server. ASP.NET has nicer mechanisms. PHP plain fails, but you can use Perl or Apache modifications to get around it.

If you need multiple file-uploads, it’s best to do each file one at a time (to overcome maximum file upload limits). Post the first form to the iframe, monitor its progress using the above and when it has finished, post the second form to the iframe, and so on.

Or use a Java/Flash solution. They’re a lot more flexible in what they can do with their posts…

See also original question in stackoverflow

#4: How do I format a Microsoft JSON date? (Score: 2064)

Created: 2008-10-15 Last updated: 2016-11-14

Tags: jquery,, ajax, json

I’m taking my first crack at Ajax with jQuery. I’m getting my data onto my page, but I’m having some trouble with the JSON data that is returned for Date data types. Basically, I’m getting a string back that looks like this:


From someone totally new to JSON - How do I format this to a short date format? Should this be handled somewhere in the jQuery code? I’ve tried the jQuery.UI.datepicker plugin using $.datepicker.formatDate() without any success.

FYI: Here’s the solution I came up with using a combination of the answers here:

function getMismatch(id) {
    { MismatchId: id },

    function (result) {

  return false;

function formatJSONDate(jsonDate) {
  var newDate = dateFormat(jsonDate, "mm/dd/yyyy");
  return newDate;

This solution got my object from the callback method and displayed the dates on the page properly using the date format library.

#4 Best answer 1 of How do I format a Microsoft JSON date? (Score: 1723)

Created: 2010-02-23 Last updated: 2021-04-27

eval() is not necessary. This will work fine:

var date = new Date(parseInt(jsonDate.substr(6)));

The substr() function takes out the /Date( part, and the parseInt() function gets the integer and ignores the )/ at the end. The resulting number is passed into the Date constructor.

I have intentionally left out the radix (the 2nd argument to parseInt); see my comment below.

Also, I completely agree with Rory’s comment: ISO-8601 dates are preferred over this old format - so this format generally shouldn’t be used for new development.

For ISO-8601 formatted JSON dates, just pass the string into the Date constructor:

var date = new Date(jsonDate); //no ugly parsing needed; full timezone support

#4 Best answer 2 of How do I format a Microsoft JSON date?(Score: 135)

Created: 2008-10-15 Last updated: 2014-11-09

You can use this to get a date from JSON:

var date = eval(jsonDate.replace(/\/Date\((\d+)\)\//gi, "new Date($1)"));

And then you can use a JavaScript Date Format script (1.2 KB when minified and gzipped) to display it as you want.

See also original question in stackoverflow

#5: Abort Ajax requests using jQuery (Score: 1895)

Created: 2009-01-15 Last updated: 2020-07-08

Tags: javascript, jquery, ajax

Is it possible that using jQuery, I cancel/abort an Ajax request that I have not yet received the response from?

#5 Best answer 1 of Abort Ajax requests using jQuery (Score: 1797)

Created: 2009-01-15 Last updated: 2018-07-14

Most of the jQuery Ajax methods return an XMLHttpRequest (or the equivalent) object, so you can just use abort().

See the documentation:

  • abort Method (MSDN). Cancels the current HTTP request.
  • abort() (MDN). If the request has been sent already, this method will abort the request.
var xhr = $.ajax({
    type: "POST",
    url: "some.php",
    data: "name=John&location=Boston",
    success: function(msg){
       alert( "Data Saved: " + msg );

//kill the request

UPDATE: As of jQuery 1.5 the returned object is a wrapper for the native XMLHttpRequest object called jqXHR. This object appears to expose all of the native properties and methods so the above example still works. See The jqXHR Object (jQuery API documentation).

UPDATE 2: As of jQuery 3, the ajax method now returns a promise with extra methods (like abort), so the above code still works, though the object being returned is not an xhr any more. See the 3.0 blog here.

UPDATE 3: xhr.abort() still works on jQuery 3.x. Don’t assume the update 2 is correct. More info on jQuery Github repository.

#5 Best answer 2 of Abort Ajax requests using jQuery(Score: 124)

Created: 2009-01-15 Last updated: 2012-07-03

You can’t recall the request but you can set a timeout value after which the response will be ignored. See this page for jquery AJAX options. I believe that your error callback will be called if the timeout period is exceeded. There is already a default timeout on every AJAX request.

You can also use the abort() method on the request object but, while it will cause the client to stop listening for the event, it may probably will not stop the server from processing it.

See also original question in stackoverflow

#6: Disable same origin policy in Chrome (Score: 1775)

Created: 2010-06-23 Last updated: 2019-05-15

Tags: javascript, ajax, google-chrome

Is there any way to disable the Same-origin policy on Google’s Chrome browser?

#6 Best answer 1 of Disable same origin policy in Chrome (Score: 1132)

Created: 2010-07-05 Last updated: 2018-06-05

Close chrome (or chromium) and restart with the --disable-web-security argument. I just tested this and verified that I can access the contents of an iframe with src=“” embedded in a page served from “localhost” (tested under chromium 5 / ubuntu). For me the exact command was:

Note : Kill all chrome instances before running command

chromium-browser --disable-web-security --user-data-dir="[some directory here]"

The browser will warn you that “you are using an unsupported command line” when it first opens, which you can ignore.

From the chromium source:

// Don't enforce the same-origin policy. (Used by people testing their sites.)
const wchar_t kDisableWebSecurity[] = L"disable-web-security";

Before Chrome 48, you could just use:

chromium-browser --disable-web-security

#6 Best answer 2 of Disable same origin policy in Chrome(Score: 1106)

Created: 2011-05-21 Last updated: 2020-06-20

Yep. For OSX, open Terminal and run:

$ open -a Google\ Chrome --args --disable-web-security --user-data-dir

–user-data-dir required on Chrome 49+ on OSX

For Linux run:

$ google-chrome --disable-web-security

Also if you’re trying to access local files for dev purposes like AJAX or JSON, you can use this flag too.


For Windows go into the command prompt and go into the folder where Chrome.exe is and type

chrome.exe --disable-web-security

That should disable the same origin policy and allow you to access local files.

Update: For Chrome 22+ you will be presented with an error message that says:

You are using an unsupported command-line flag: –disable-web-security. Stability and security will suffer.

However you can just ignore that message while developing.

See also original question in stackoverflow

#7: How to manage a redirect request after a jQuery Ajax call (Score: 1433)

Created: 2008-10-13 Last updated: 2016-01-22

Tags: javascript, jquery, ajax, redirect

I’m using $.post() to call a servlet using Ajax and then using the resulting HTML fragment to replace a div element in the user’s current page. However, if the session times out, the server sends a redirect directive to send the user to the login page. In this case, jQuery is replacing the div element with the contents of the login page, forcing the user’s eyes to witness a rare scene indeed.

How can I manage a redirect directive from an Ajax call with jQuery 1.2.6?

#7 Best answer 1 of How to manage a redirect request after a jQuery Ajax call (Score: 718)

Created: 2009-10-07 Last updated: 2019-10-29

I read this question and implemented the approach that has been stated regarding setting the response HTTP status code to 278 in order to avoid the browser transparently handling the redirects. Even though this worked, I was a little dissatisfied as it is a bit of a hack.

After more digging around, I ditched this approach and used JSON. In this case, all responses to AJAX requests have the status code 200 and the body of the response contains a JSON object that is constructed on the server. The JavaScript on the client can then use the JSON object to decide what it needs to do.

I had a similar problem to yours. I perform an AJAX request that has 2 possible responses: one that redirects the browser to a new page and one that replaces an existing HTML form on the current page with a new one. The jQuery code to do this looks something like:

    type: "POST",
    url: reqUrl,
    data: reqBody,
    dataType: "json",
    success: function(data, textStatus) {
        if (data.redirect) {
            // data.redirect contains the string URL to redirect to
            window.location.href = data.redirect;
        } else {
            // data.form contains the HTML for the replacement form

The JSON object “data” is constructed on the server to have 2 members: data.redirect and data.form. I found this approach to be much better.

#7 Best answer 2 of How to manage a redirect request after a jQuery Ajax call(Score: 256)

Created: 2009-02-23 Last updated: 2017-11-08

I solved this issue by:

  1. Adding a custom header to the response:

    public ActionResult Index(){
        if (!HttpContext.User.Identity.IsAuthenticated)
        return View();
  2. Binding a JavaScript function to the ajaxSuccess event and checking to see if the header exists:

    $(document).ajaxSuccess(function(event, request, settings) {
        if (request.getResponseHeader('REQUIRES_AUTH') === '1') {
           window.location = '/';

See also original question in stackoverflow

#8: How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request? (Score: 1253)

Created: 2008-09-25 Last updated: 2018-05-22

Tags: javascript, jquery, ajax, asynchronous

I have a JavaScript widget which provides standard extension points. One of them is the beforecreate function. It should return false to prevent an item from being created.

I’ve added an Ajax call into this function using jQuery:

beforecreate: function (node, targetNode, type, to) {
  jQuery.get('' + + '?name=' + encode(to.inp[0].value),

  function (result) {
    if (result.isOk == false) 

But I want to prevent my widget from creating the item, so I should return false in the mother-function, not in the callback. Is there a way to perform a synchronous AJAX request using jQuery or any other in-browser API?

#8 Best answer 1 of How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request? (Score: 1191)

Created: 2008-09-25 Last updated: 2020-11-16

From the jQuery documentation: you specify the asynchronous option to be false to get a synchronous Ajax request. Then your callback can set some data before your mother function proceeds.

Here’s what your code would look like if changed as suggested:

beforecreate: function (node, targetNode, type, to) {
        url: '' + + '?name=' + encode(to.inp[0].value),
        success: function (result) {
            if (result.isOk == false) alert(result.message);
        async: false

#8 Best answer 2 of How can I get jQuery to perform a synchronous, rather than asynchronous, Ajax request?(Score: 261)

Created: 2011-04-12 Last updated: 2018-03-30

You can put the jQuery’s Ajax setup in synchronous mode by calling


And then perform your Ajax calls using jQuery.get( ... );

Then just turning it on again once


I guess it works out the same thing as suggested by @Adam, but it might be helpful to someone that does want to reconfigure their jQuery.get() or to the more elaborate jQuery.ajax() syntax.

See also original question in stackoverflow

#9: How to manually send HTTP POST requests from Firefox or Chrome browser? (Score: 1233)

Created: 2011-01-25 Last updated: 2020-06-11

Tags: ajax, google-chrome, firefox, browser, http-post

I want to test some URLs on a web application I’m working on. For that I would like to manually create HTTP POST requests (meaning I can add whatever parameters I like).

Is there any extension or functionality in Chrome and/or Firefox that I’m missing?

#9 Best answer 1 of How to manually send HTTP POST requests from Firefox or Chrome browser? (Score: 2390)

Created: 2012-03-15 Last updated: 2021-03-17

I have been making a Chrome app called Postman for this type of stuff. All the other extensions seemed a bit dated so made my own. It also has a bunch of other features which have been helpful for documenting our own API here.

Postman now also has native apps (i.e. standalone) for Windows, Mac and Linux! It is more preferable now to use native apps, read more here.

#9 Best answer 2 of How to manually send HTTP POST requests from Firefox or Chrome browser?(Score: 405)

Created: 2013-06-01 Last updated: 2018-12-20

CURL is AWESOME to do what you want ! It’s a simple but effective command line tool.

Rest implementation test commands :

curl -i -X GET
curl -i -X GET
curl -i -X DELETE
curl -i -X POST -H 'Content-Type: application/json' -d '{"name": "New item", "year": "2009"}'
curl -i -X PUT -H 'Content-Type: application/json' -d '{"name": "Updated item", "year": "2010"}'

See also original question in stackoverflow

#10: Serializing to JSON in jQuery (Score: 1214)

Created: 2008-10-10 Last updated: 2019-07-03

Tags: javascript, jquery, ajax, json, serialization

I need to serialize an object to JSON. I’m using jQuery. Is there a “standard” way to do this?

My specific situation: I have an array defined as shown below:

var countries = new Array();
countries[0] = 'ga';
countries[1] = 'cd';

and I need to turn this into a string to pass to $.ajax() like this:

    type: "POST",
    url: "Concessions.aspx/GetConcessions",
    data: "{'countries':['ga','cd']}",

#10 Best answer 1 of Serializing to JSON in jQuery (Score: 1149)

Created: 2009-05-26 Last updated: 2019-05-15

JSON-js - JSON in JavaScript.

To convert an object to a string, use JSON.stringify:

var json_text = JSON.stringify(your_object, null, 2);

To convert a JSON string to object, use JSON.parse:

var your_object = JSON.parse(json_text);

It was recently recommended by John Resig:

…PLEASE start migrating your JSON-using applications over to Crockford’s json2.js. It is fully compatible with the ECMAScript 5 specification and gracefully degrades if a native (faster!) implementation exists.

In fact, I just landed a change in jQuery yesterday that utilizes the JSON.parse method if it exists, now that it has been completely specified.

I tend to trust what he says on JavaScript matters :)

All modern browsers (and many older ones which aren’t ancient) support the JSON object natively. The current version of Crockford’s JSON library will only define JSON.stringify and JSON.parse if they’re not already defined, leaving any browser native implementation intact.

#10 Best answer 2 of Serializing to JSON in jQuery(Score: 185)

Created: 2011-06-01

I’ve been using jquery-json for 6 months and it works great. It’s very simple to use:

var myObj = {foo: "bar", "baz": "wockaflockafliz"};

// Result: {"foo":"bar","baz":"wockaflockafliz"}

See also original question in stackoverflow

  1. This page use API to get the relevant data from stackoverflow community.
  2. Content license on this page is CC BY-SA 3.0.
  3. score = up votes - down votes.