Error ajax call jquery

The $.ajax() function underlies all Ajax requests sent by jQuery. It is often unnecessary to directly call this function, as several higher-level alternatives like $.get() and .load() are available and are easier to use. If less common options are required, though, $.ajax() can be used more flexibly.

At its simplest, the $.ajax() function can be called with no arguments:

Note: Default settings can be set globally by using the $.ajaxSetup() function.

This example, using no options, loads the contents of the current page, but does nothing with the result. To use the result, you can implement one of the callback functions.

The jqXHR Object

The jQuery XMLHttpRequest (jqXHR) object returned by $.ajax() as of jQuery 1.5 is a superset of the browser’s native XMLHttpRequest object. For example, it contains responseText and responseXML properties, as well as a getResponseHeader() method. When the transport mechanism is something other than XMLHttpRequest (for example, a script tag for a JSONP request) the jqXHR object simulates native XHR functionality where possible.

As of jQuery 1.5.1, the jqXHR object also contains the overrideMimeType() method (it was available in jQuery 1.4.x, as well, but was temporarily removed in jQuery 1.5). The .overrideMimeType() method may be used in the beforeSend() callback function, for example, to modify the response content-type header:

  url: "https://fiddle.jshell.net/favicon.png",
  beforeSend: function( xhr ) {
    xhr.overrideMimeType( "text/plain; charset=x-user-defined" );
    if ( console && console.log ) {
      console.log( "Sample of data:", data.slice( 0, 100 ) );

The jqXHR objects returned by $.ajax() as of jQuery 1.5 implement the Promise interface, giving them all the properties, methods, and behavior of a Promise (see Deferred object for more information). These methods take one or more function arguments that are called when the $.ajax() request terminates. This allows you to assign multiple callbacks on a single request, and even to assign callbacks after the request may have completed. (If the request is already complete, the callback is fired immediately.) Available Promise methods of the jqXHR object include:

• jqXHR.done(function( data, textStatus, jqXHR ) {});

  An alternative construct to the success callback option, refer to deferred.done() for implementation details.

• jqXHR.fail(function( jqXHR, textStatus, errorThrown ) {});

  An alternative construct to the error callback option, the .fail() method replaces the deprecated .error() method. Refer to deferred.fail() for implementation details.

• jqXHR.always(function( data|jqXHR, textStatus, jqXHR|errorThrown ) { }); (added in jQuery 1.6)

  An alternative construct to the complete callback option, the .always() method replaces the deprecated .complete() method.

  In response to a successful request, the function’s arguments are the same as those of .done(): data, textStatus, and the jqXHR object. For failed requests the arguments are the same as those of .fail(): the jqXHR object, textStatus, and errorThrown. Refer to deferred.always() for implementation details.

• jqXHR.then(function( data, textStatus, jqXHR ) {}, function( jqXHR, textStatus, errorThrown ) {});

  Incorporates the functionality of the .done() and .fail() methods, allowing (as of jQuery 1.8) the underlying Promise to be manipulated. Refer to deferred.then() for implementation details.

Deprecation Notice: The jqXHR.success(), jqXHR.error(), and jqXHR.complete() callbacks are removed as of jQuery 3.0. You can use jqXHR.done(), jqXHR.fail(), and jqXHR.always() instead.

// Assign handlers immediately after making the request,
// and remember the jqXHR object for this request



  


                       
  



var jqxhr = $.ajax( "example.php" )
// Perform other work here ...
// Set another completion function for the request above
jqxhr.always(function() {
  alert( "second complete" );

The this reference within all callbacks is the object in the context option passed to $.ajax in the settings; if context is not specified, this is a reference to the Ajax settings themselves.

For backward compatibility with XMLHttpRequest, a jqXHR object will expose the following properties and methods:

• readyState
• responseXML and/or responseText when the underlying request responded with xml and/or text, respectively
• status
• statusText (may be an empty string in HTTP/2)
• abort( [ statusText ] )
• getAllResponseHeaders() as a string
• getResponseHeader( name )
• overrideMimeType( mimeType )
• setRequestHeader( name, value ) which departs from the standard by replacing the old value with the new one rather than concatenating the new value to the old one
• statusCode( callbacksByStatusCode )

No onreadystatechange mechanism is provided, however, since done, fail, always, and statusCode cover all conceivable requirements.

Callback Function Queues

The beforeSend, error, dataFilter, success and complete options all accept callback functions that are invoked at the appropriate times.

As of jQuery 1.5, the fail and done, and, as of jQuery 1.6, always callback hooks are first-in, first-out managed queues, allowing for more than one callback for each hook. See Deferred object methods, which are implemented internally for these $.ajax() callback hooks.

The callback hooks provided by $.ajax() are as follows:

1. beforeSend callback option is invoked; it receives the jqXHR object and the settings object as parameters.
2. error callback option is invoked, if the request fails. It receives the jqXHR, a string indicating the error type, and an exception object if applicable. Some built-in errors will provide a string as the exception object: «abort», «timeout», «No Transport».
3. dataFilter callback option is invoked immediately upon successful receipt of response data. It receives the returned data and the value of dataType, and must return the (possibly altered) data to pass on to success.
4. success callback option is invoked, if the request succeeds. It receives the returned data, a string containing the success code, and the jqXHR object.
5. Promise callbacks — .done(), .fail(), .always(), and .then() — are invoked, in the order they are registered.
6. complete callback option fires, when the request finishes, whether in failure or success. It receives the jqXHR object, as well as a string containing the success or error code.

Data Types

Different types of response to $.ajax() call are subjected to different kinds of pre-processing before being passed to the success handler. The type of pre-processing depends by default upon the Content-Type of the response, but can be set explicitly using the dataType option. If the dataType option is provided, the Content-Type header of the response will be disregarded.

The available data types are text, html, xml, json, jsonp, and script.

If text or html is specified, no pre-processing occurs. The data is simply passed on to the success handler, and made available through the responseText property of the jqXHR object.

If xml is specified, the response is parsed using jQuery.parseXML before being passed, as an XMLDocument, to the success handler. The XML document is made available through the responseXML property of the jqXHR object.

If json is specified, the response is parsed using jQuery.parseJSON before being passed, as an object, to the success handler. The parsed JSON object is made available through the responseJSON property of the jqXHR object.

If script is specified, $.ajax() will execute the JavaScript that is received from the server before passing it on to the success handler as a string.

If jsonp is specified, $.ajax() will automatically append a query string parameter of (by default) callback=? to the URL. The jsonp and jsonpCallback properties of the settings passed to $.ajax() can be used to specify, respectively, the name of the query string parameter and the name of the JSONP callback function. The server should return valid JavaScript that passes the JSON response into the callback function. $.ajax() will execute the returned JavaScript, calling the JSONP callback function, before passing the JSON object contained in the response to the $.ajax() success handler.

For more information on JSONP, see the original post detailing its use.

Sending Data to the Server

By default, Ajax requests are sent using the GET HTTP method. If the POST method is required, the method can be specified by setting a value for the type option. This option affects how the contents of the data option are sent to the server. POST data will always be transmitted to the server using UTF-8 charset, per the W3C XMLHTTPRequest standard.

The data option can contain either a query string of the form key1=value1&key2=value2, or an object of the form {key1: 'value1', key2: 'value2'}. If the latter form is used, the data is converted into a query string using jQuery.param() before it is sent. This processing can be circumvented by setting processData to false. The processing might be undesirable if you wish to send an XML object to the server; in this case, change the contentType option from application/x-www-form-urlencoded to a more appropriate MIME type.

Advanced Options

The global option prevents handlers registered using .ajaxSend(), .ajaxError(), and similar methods from firing when this request would trigger them. This can be useful to, for example, suppress a loading indicator that was implemented with .ajaxSend() if the requests are frequent and brief. With cross-domain script and JSONP requests, the global option is automatically set to false. See the descriptions of these methods below for more details.

If the server performs HTTP authentication before providing a response, the user name and password pair can be sent via the username and password options.

Ajax requests are time-limited, so errors can be caught and handled to provide a better user experience. Request timeouts are usually either left at their default or set as a global default using $.ajaxSetup() rather than being overridden for specific requests with the timeout option.

By default, requests are always issued, but the browser may serve results out of its cache. To disallow use of the cached results, set cache to false. To cause the request to report failure if the asset has not been modified since the last request, set ifModified to true.

The scriptCharset allows the character set to be explicitly specified for requests that use a <script> tag (that is, a type of script or jsonp). This is useful if the script and host page have differing character sets.

The first letter in Ajax stands for «asynchronous,» meaning that the operation occurs in parallel and the order of completion is not guaranteed. The async option to $.ajax() defaults to true, indicating that code execution can continue after the request is made. Setting this option to false (and thus making the call no longer asynchronous) is strongly discouraged, as it can cause the browser to become unresponsive.

The $.ajax() function returns the XMLHttpRequest object that it creates. Normally jQuery handles the creation of this object internally, but a custom function for manufacturing one can be specified using the xhr option. The returned object can generally be discarded, but does provide a lower-level interface for observing and manipulating the request. In particular, calling .abort() on the object will halt the request before it completes.

Extending Ajax

As of jQuery 1.5, jQuery’s Ajax implementation includes prefilters, transports, and converters that allow you to extend Ajax with a great deal of flexibility.

Using Converters

$.ajax() converters support mapping data types to other data types. If, however, you want to map a custom data type to a known type (e.g json), you must add a correspondence between the response Content-Type and the actual data type using the contents option:

    mycustomtype: /mycustomtype/
    "mycustomtype json": function( result ) {

This extra object is necessary because the response Content-Types and data types never have a strict one-to-one correspondence (hence the regular expression).

To convert from a supported type (e.g text, json) to a custom data type and back again, use another pass-through converter:

    mycustomtype: /mycustomtype/
    "text mycustomtype": true,
    "mycustomtype json": function( result ) {



  


                       
  

The above now allows passing from text to mycustomtype and then mycustomtype to json.

Let’s say I have the following jQuery AJAX call:

$.ajax({
   type: "POST",
   url: "MyUrl",
   data: "val1=test",
   success: function(result){
        // Do stuff
   }
 });

Now, when this AJAX call is made I want the server-side code to run through a few error handling checks (e.g. is the user still logged in, do they have permission to use this call, is the data valid, etc). If an error is detected, how do I bubble that error message back up to the client side?

My initial thought would be to return a JSON object with two fields: error and errorMessage. These fields would then be checked in the jQuery AJAX call:

$.ajax({
   type: "POST",
   url: "MyUrl",
   data: "val1=test",
   success: function(result){
       if (result.error == "true") 
       {
           alert("An error occurred: " & result.errorMessage);
       }
       else 
       {
           // Do stuff
       }
   }
 });

This feels a bit clunky to me, but it works. Is there a better alternative?

This is a tutorial on how to handle errors when making Ajax requests via the jQuery library. A lot of developers seem to assume that their Ajax requests will always succeed. However, in certain cases, the request may fail and you will need to inform the user.

Here is some sample JavaScript code where I use the jQuery library to send an Ajax request to a PHP script that does not exist:

$.ajax({
     url: 'does-not-exist.php',
     success: function(returnData){
         var res = JSON.parse(returnData);
     },
     error: function(xhr, status, error){
         var errorMessage = xhr.status + ': ' + xhr.statusText
         alert('Error - ' + errorMessage);
     }
});

If you look at the code above, you will notice that I have two functions:

• success: The success function is called if the Ajax request is completed successfully. i.e. If the server returns a HTTP status of 200 OK. If our request fails because the server responded with an error, then the success function will not be executed.
• error: The error function is executed if the server responds with a HTTP error. In the example above, I am sending an Ajax request to a script that I know does not exist. If I run the code above, the error function will be executed and a JavaScript alert message will pop up and display information about the error.

The Ajax error function has three parameters:

• jqXHR
• textStatus
• errorThrown

In truth, the jqXHR object will give you all of the information that you need to know about the error that just occurred. This object will contain two important properties:

• status: This is the HTTP status code that the server returned. If you run the code above, you will see that this is 404. If an Internal Server Error occurs, then the status property will be 500.
• statusText: If the Ajax request fails, then this property will contain a textual representation of the error that just occurred. If the server encounters an error, then this will contain the text “Internal Server Error”.

Obviously, in most cases, you will not want to use an ugly JavaScript alert message. Instead, you would create an error message and display it above the Ajax form that the user is trying to submit.

JQuery 3.0: The error, success and complete callbacks are deprecated.

Update: As of JQuery 3.0, the success, error and complete callbacks have all been removed. As a result, you will have to use the done, fail and always callbacks instead.

An example of done and fail being used:

$.ajax("submit.php")
  .done(function(data) {
      //Ajax request was successful.
  })
  .fail(function(xhr, status, error) {
      //Ajax request failed.
      var errorMessage = xhr.status + ': ' + xhr.statusText
      alert('Error - ' + errorMessage);
})

Note that always is like complete, in the sense that it will always be called, regardless of whether the request was successful or not.

Hopefully, you found this tutorial to be useful.

jQuery.ajax()

jQuery.ajax( url [, settings ] ) Returns: jqXHR

Description: Perform an asynchronous HTTP (Ajax) request.

version added: 1.5 jQuery.ajax( url [, settings ] )

version added: 1.0 jQuery.ajax( [settings ] )

Data to be sent to the server. If the HTTP method is one that cannot have an entity body, such as GET, the data is appended to the URL.

When data is an object, jQuery generates the data string from the object’s key/value pairs unless the processData option is set to false . For example, < a: «bc», d: «e,f» >is converted to the string «a=bc&d=e%2Cf» . If the value is an array, jQuery serializes multiple values with same key based on the value of the traditional setting (described below). For example, < a: [1,2] >becomes the string «a%5B%5D=1&a%5B%5D=2» with the default traditional: false setting.

When data is passed as a string it should already be encoded using the correct encoding for contentType , which by default is application/x-www-form-urlencoded .

In requests with dataType: «json» or dataType: «jsonp» , if the string contains a double question mark ( ?? ) anywhere in the URL or a single question mark ( ? ) in the query string, it is replaced with a value generated by jQuery that is unique for each copy of the library on the page (e.g. jQuery21406515378922229067_1479880736745 ).

An object of numeric HTTP codes and functions to be called when the response has the corresponding code. For example, the following will alert when the response status is a 404:

If the request is successful, the status code functions take the same parameters as the success callback; if it results in an error (including 3xx redirect), they take the same parameters as the error callback.

In jQuery 1.5, the withCredentials property was not propagated to the native XHR and thus CORS requests requiring it would ignore this flag. For this reason, we recommend using jQuery 1.5.1+ should you require the use of it.

The $.ajax() function underlies all Ajax requests sent by jQuery. It is often unnecessary to directly call this function, as several higher-level alternatives like $.get() and .load() are available and are easier to use. If less common options are required, though, $.ajax() can be used more flexibly.

At its simplest, the $.ajax() function can be called with no arguments:

Note: Default settings can be set globally by using the $.ajaxSetup() function.

This example, using no options, loads the contents of the current page, but does nothing with the result. To use the result, you can implement one of the callback functions.

The jqXHR Object

The jQuery XMLHttpRequest (jqXHR) object returned by $.ajax() as of jQuery 1.5 is a superset of the browser’s native XMLHttpRequest object. For example, it contains responseText and responseXML properties, as well as a getResponseHeader() method. When the transport mechanism is something other than XMLHttpRequest (for example, a script tag for a JSONP request) the jqXHR object simulates native XHR functionality where possible.

As of jQuery 1.5.1, the jqXHR object also contains the overrideMimeType() method (it was available in jQuery 1.4.x, as well, but was temporarily removed in jQuery 1.5). The .overrideMimeType() method may be used in the beforeSend() callback function, for example, to modify the response content-type header:

The jqXHR objects returned by $.ajax() as of jQuery 1.5 implement the Promise interface, giving them all the properties, methods, and behavior of a Promise (see Deferred object for more information). These methods take one or more function arguments that are called when the $.ajax() request terminates. This allows you to assign multiple callbacks on a single request, and even to assign callbacks after the request may have completed. (If the request is already complete, the callback is fired immediately.) Available Promise methods of the jqXHR object include:

jqXHR.done(function( data, textStatus, jqXHR ) <>);

An alternative construct to the success callback option, refer to deferred.done() for implementation details.

jqXHR.fail(function( jqXHR, textStatus, errorThrown ) <>);

An alternative construct to the error callback option, the .fail() method replaces the deprecated .error() method. Refer to deferred.fail() for implementation details.

jqXHR.always(function( data|jqXHR, textStatus, jqXHR|errorThrown ) < >); (added in jQuery 1.6)

An alternative construct to the complete callback option, the .always() method replaces the deprecated .complete() method.

In response to a successful request, the function’s arguments are the same as those of .done() : data, textStatus, and the jqXHR object. For failed requests the arguments are the same as those of .fail() : the jqXHR object, textStatus, and errorThrown. Refer to deferred.always() for implementation details.

jqXHR.then(function( data, textStatus, jqXHR ) <>, function( jqXHR, textStatus, errorThrown ) <>);

Incorporates the functionality of the .done() and .fail() methods, allowing (as of jQuery 1.8) the underlying Promise to be manipulated. Refer to deferred.then() for implementation details.

Deprecation Notice: The jqXHR.success() , jqXHR.error() , and jqXHR.complete() callbacks are removed as of jQuery 3.0. You can use jqXHR.done() , jqXHR.fail() , and jqXHR.always() instead.

The this reference within all callbacks is the object in the context option passed to $.ajax in the settings; if context is not specified, this is a reference to the Ajax settings themselves.

For backward compatibility with XMLHttpRequest , a jqXHR object will expose the following properties and methods:

• readyState
• responseXML and/or responseText when the underlying request responded with xml and/or text, respectively
• status
• statusText (may be an empty string in HTTP/2)
• abort( [ statusText ] )
• getAllResponseHeaders() as a string
• getResponseHeader( name )
• overrideMimeType( mimeType )
• setRequestHeader( name, value ) which departs from the standard by replacing the old value with the new one rather than concatenating the new value to the old one
• statusCode( callbacksByStatusCode )

No onreadystatechange mechanism is provided, however, since done , fail , always , and statusCode cover all conceivable requirements.

Callback Function Queues

The beforeSend , error , dataFilter , success and complete options all accept callback functions that are invoked at the appropriate times.

As of jQuery 1.5, the fail and done , and, as of jQuery 1.6, always callback hooks are first-in, first-out managed queues, allowing for more than one callback for each hook. See Deferred object methods, which are implemented internally for these $.ajax() callback hooks.

The callback hooks provided by $.ajax() are as follows:

1. beforeSend callback option is invoked; it receives the jqXHR object and the settings object as parameters.
2. error callback option is invoked, if the request fails. It receives the jqXHR , a string indicating the error type, and an exception object if applicable. Some built-in errors will provide a string as the exception object: «abort», «timeout», «No Transport».
3. dataFilter callback option is invoked immediately upon successful receipt of response data. It receives the returned data and the value of dataType , and must return the (possibly altered) data to pass on to success .
4. success callback option is invoked, if the request succeeds. It receives the returned data, a string containing the success code, and the jqXHR object.
5. Promise callbacks — .done() , .fail() , .always() , and .then() — are invoked, in the order they are registered.
6. complete callback option fires, when the request finishes, whether in failure or success. It receives the jqXHR object, as well as a string containing the success or error code.

Data Types

Different types of response to $.ajax() call are subjected to different kinds of pre-processing before being passed to the success handler. The type of pre-processing depends by default upon the Content-Type of the response, but can be set explicitly using the dataType option. If the dataType option is provided, the Content-Type header of the response will be disregarded.

The available data types are text , html , xml , json , jsonp , and script .

If text or html is specified, no pre-processing occurs. The data is simply passed on to the success handler, and made available through the responseText property of the jqXHR object.

If xml is specified, the response is parsed using jQuery.parseXML before being passed, as an XMLDocument , to the success handler. The XML document is made available through the responseXML property of the jqXHR object.

If json is specified, the response is parsed using jQuery.parseJSON before being passed, as an object, to the success handler. The parsed JSON object is made available through the responseJSON property of the jqXHR object.

If script is specified, $.ajax() will execute the JavaScript that is received from the server before passing it on to the success handler as a string.

If jsonp is specified, $.ajax() will automatically append a query string parameter of (by default) callback=? to the URL. The jsonp and jsonpCallback properties of the settings passed to $.ajax() can be used to specify, respectively, the name of the query string parameter and the name of the JSONP callback function. The server should return valid JavaScript that passes the JSON response into the callback function. $.ajax() will execute the returned JavaScript, calling the JSONP callback function, before passing the JSON object contained in the response to the $.ajax() success handler.

For more information on JSONP, see the original post detailing its use.

Sending Data to the Server

By default, Ajax requests are sent using the GET HTTP method. If the POST method is required, the method can be specified by setting a value for the type option. This option affects how the contents of the data option are sent to the server. POST data will always be transmitted to the server using UTF-8 charset, per the W3C XMLHTTPRequest standard.

Advanced Options

The global option prevents handlers registered using .ajaxSend() , .ajaxError() , and similar methods from firing when this request would trigger them. This can be useful to, for example, suppress a loading indicator that was implemented with .ajaxSend() if the requests are frequent and brief. With cross-domain script and JSONP requests, the global option is automatically set to false . See the descriptions of these methods below for more details.

If the server performs HTTP authentication before providing a response, the user name and password pair can be sent via the username and password options.

Ajax requests are time-limited, so errors can be caught and handled to provide a better user experience. Request timeouts are usually either left at their default or set as a global default using $.ajaxSetup() rather than being overridden for specific requests with the timeout option.

By default, requests are always issued, but the browser may serve results out of its cache. To disallow use of the cached results, set cache to false . To cause the request to report failure if the asset has not been modified since the last request, set ifModified to true .

The scriptCharset allows the character set to be explicitly specified for requests that use a

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.ajaxError()

.ajaxError( handler ) Returns: jQuery

Description: Register a handler to be called when Ajax requests complete with an error. This is an Ajax Event.

version added: 1.0 .ajaxError( handler )

Whenever an Ajax request completes with an error, jQuery triggers the ajaxError event. Any and all handlers that have been registered with the .ajaxError() method are executed at this time. Note: This handler is not called for cross-domain script and cross-domain JSONP requests.

To observe this method in action, set up a basic Ajax load request.

Attach the event handler to the document:

Now, make an Ajax request using any jQuery method:

When the user clicks the button and the Ajax request fails, because the requested file is missing, the log message is displayed.

All ajaxError handlers are invoked, regardless of what Ajax request was completed. To differentiate between the requests, use the parameters passed to the handler. Each time an ajaxError handler is executed, it is passed the event object, the jqXHR object (prior to jQuery 1.5, the XHR object), and the settings object that was used in the creation of the request. When an HTTP error occurs, the fourth argument ( thrownError ) receives the textual portion of the HTTP status, such as «Not Found» or «Internal Server Error.» For example, to restrict the error callback to only handling events dealing with a particular URL:

Additional Notes:

• As of jQuery 1.9, all the handlers for the jQuery global Ajax events, including those added with the .ajaxError() method, must be attached to document .
• If $.ajax() or $.ajaxSetup() is called with the global option set to false , the .ajaxError() method will not fire.

Example:

Show a message when an Ajax request fails.

Books

Copyright 2023 OpenJS Foundation and jQuery contributors. All rights reserved. See jQuery License for more information. The OpenJS Foundation has registered trademarks and uses trademarks. For a list of trademarks of the OpenJS Foundation, please see our Trademark Policy and Trademark List. Trademarks and logos not indicated on the list of OpenJS Foundation trademarks are trademarks™ or registered® trademarks of their respective holders. Use of them does not imply any affiliation with or endorsement by them. OpenJS Foundation Terms of Use, Privacy, and Cookie Policies also apply. Web hosting by Digital Ocean | CDN by StackPath

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Handling Ajax errors with jQuery.

This is a tutorial on how to handle errors when making Ajax requests via the jQuery library. A lot of developers seem to assume that their Ajax requests will always succeed. However, in certain cases, the request may fail and you will need to inform the user.

Here is some sample JavaScript code where I use the jQuery library to send an Ajax request to a PHP script that does not exist:

If you look at the code above, you will notice that I have two functions:

• success: The success function is called if the Ajax request is completed successfully. i.e. If the server returns a HTTP status of 200 OK. If our request fails because the server responded with an error, then the success function will not be executed.
• error: The error function is executed if the server responds with a HTTP error. In the example above, I am sending an Ajax request to a script that I know does not exist. If I run the code above, the error function will be executed and a JavaScript alert message will pop up and display information about the error.

The Ajax error function has three parameters:

In truth, the jqXHR object will give you all of the information that you need to know about the error that just occurred. This object will contain two important properties:

• status: This is the HTTP status code that the server returned. If you run the code above, you will see that this is 404. If an Internal Server Error occurs, then the status property will be 500.
• statusText: If the Ajax request fails, then this property will contain a textual representation of the error that just occurred. If the server encounters an error, then this will contain the text “Internal Server Error”.

Obviously, in most cases, you will not want to use an ugly JavaScript alert message. Instead, you would create an error message and display it above the Ajax form that the user is trying to submit.

JQuery 3.0: The error, success and complete callbacks are deprecated.

Update: As of JQuery 3.0, the success, error and complete callbacks have all been removed. As a result, you will have to use the done, fail and always callbacks instead.

An example of done and fail being used:

Note that always is like complete, in the sense that it will always be called, regardless of whether the request was successful or not.

Hopefully, you found this tutorial to be useful.

One thought on “ Handling Ajax errors with jQuery. ”

thanks its helpful 🙂 many of us not aware of error block in ajax

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In this article I will explain how to display the error messages and details of error exceptions caught inside the Error and Failure event handlers of jQuery AJAX call.

The error messages and details are displayed using jQuery UI Dialog Popup.

There are two types of Exceptions which is caught by jQuery

1. When exception object is in the form of JSON object.

2. When exception object is in the form of plain text or HTML.

I will explain both the types with detailed explanation and also how to display the exception error details in both the cases.

WebMethod for testing both types

In order to test both the cases I have created the following WebMethod which simply tries to convert the received string value to integer.

1. When exception object is in the form of JSON object

In the following HTML Markup, I have created a simple form with a TextBox and a Button which prompts user to enter a Numeric value.

The value entered is passed to the WebMethod using a jQuery AJAX call where it is converts string value to integer.

If it is a valid number then an alert message is displayed inside the jQuery AJAX Success event handler and if an exception occurs in the WebMethod, the thrown exception is caught inside the jQuery AJAX Error event handler and which makes a call to the OnError JavaScript function which processes and displays the exception details.

2. When exception object is in the form of HTML or plain text

The second case is similar to the first one. In order to receive a Non-JSON response I have just set incorrect WebMethod name in the jQuery AJAX so that it generates an error.

Parsing the received Exception response using jQuery

Here I am explaining the details of the OnError JavaScript function which is called by the Error event handler in both the above case.

This function accepts the following three parameters

xhr – It is the error response object.

errorType – It describes the type of error.

exception – It contains the title of the exception occurred.

Inside this function, I have placed a TRY CATCH block and within the TRY block, the Exception received is parsed to a JSON object and then the details of the exception are displayed using jQuery Dialog Modal Popup.

If an error occurs during the process of parsing the JSON string, it means it is a Non-JSON response i.e. HTML or plain text and then it is handled inside the CATCH block where I am displaying the exception directly without any processing.

Demo

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Функция $.ajax() лежит в основе всех Ajax запросов отправляемых при помощи jQuery. Зачастую нет необходимости вызывать эту функцию, так как есть несколько альтернатив более высого уровня, такие как $.get() и .load(), которые более простые в использовании. Если требуется менее распространенные варианты , через, $.ajax() Вы можете более гибко скофигурировать запрос.

В простейшем виде, функция $.ajax() может быть вызвана без аргументов:

Важно: настройки по умолчанию могут быть установлены при помощи функции $.ajaxSetup().

Этот пример, не используюя никаких параметров, загружает содержимое текущей страницы, но ничего не делает с результатом. Для использования результата, Вы можете реализовать одну из функция обратного вызова.

Объект jqXHR

Объект jQuery XMLHttpRequest (jqXHR) возвращается функцией $.ajax() начиная с jQuery 1.5 является надстройкой над нативным объектом XMLHttpRequest. Например, он содержит свойства responseText и responseXML, а также метод getResponseHeader(). Когда траспортом используемым для запрос является что то иное, а не XMLHttpRequest (например, тэг script tag для JSONP запроса) объект jqXHR эмулирует функционал нативного XHR там где это возможно.

Начиная с jQuery 1.5.1, объект jqXHR также содержит метод overrideMimeType() (он был доступен в jQuery 1.4.x, но был временно удален в версии jQuery 1.5). Метод .overrideMimeType() может быть использован в обработчике beforeSend(), например, для изменения поля заголовка content-type:

  url: "http://fiddle.jshell.net/favicon.png",
  beforeSend: function( xhr ) {
    xhr.overrideMimeType( "text/plain; charset=x-user-defined" );
    if ( console && console.log ) {
      console.log( "Sample of data:", data.slice( 0, 100 ) );

Объект jqXHR возвращаемый методом $.ajax() в версии jQuery 1.5 реализует интерфейс Promise, дающий ему все свойства, методы и поведение Promise. Эти методы принимают один или несколько аргументов, которые вызываются при завершении запроса инициированного при помощи $.ajax(). Это позволяет назначать несколько обработчиков на один запрос и даже назначать обработчики после того как запрос может быть завершен. (Если запрос уже выполнен, то обработчики вызовутся немедленно). Доступные методы Promise в объекте jqXHR:

• jqXHR.done(function( data, textStatus, jqXHR ) {});

  Альтернатива создания обработчика success, подробнее смотрите на deferred.done().

• jqXHR.fail(function( jqXHR, textStatus, errorThrown ) {});

  Альтернатива создания обработчика error, метод .fail() заменяет устаревший метод .error(). Смотрите подробнее deferred.fail().

• jqXHR.always(function( data|jqXHR, textStatus, jqXHR|errorThrown ) { }); (добавлен в версии jQuery 1.6)

  Альтернатива создания обработчика complete, метод .always() заменяет устаревший метод .complete().

  В ответ на успешный запрос, аргументы функции те же самые что и у .done(): data, textStatus и объект jqXHR. Для ошибочных зпросов аргументы те же самые что и у .fail(): объект jqXHR, textStatus и errorThrown. Смотрите подробнее deferred.always().

• jqXHR.then(function( data, textStatus, jqXHR ) {}, function( jqXHR, textStatus, errorThrown ) {});

  Включает в себя функциональность методов .done() и .fail(), что упрощает (начиная с jQuery 1.8) проще управлять объектом Promise. Смотрите подробнее deferred.then().

Внимание: обработчики jqXHR.success(), jqXHR.error() и jqXHR.complete() будут удалены в jQuery 3.0. Вы можете использовать jqXHR.done(), jqXHR.fail() и jqXHR.always() соответственно.

// Назначаем обработчики сразу после выполнения запроса
// и сохраняем объект jqXHR для этого запроса
var jqxhr = $.ajax( "example.php" )
// Установим другой обработчик выполнения запроса
jqxhr.always(function() {
  alert( "second complete" );

Ссылка this внутри всех обработчиков указывает на объект заданный в параметре context переданные в аргумент settings метода $.ajax; если context не указан, то this указывает на объект settings.

Для обеспечения обратной совместимости с кодом XMLHttpRequest, в объекте jqXHR предоставляет следующие свойства и методы:

• readyState
• status
• statusText
• responseXML и/или responseText когда запрос вернул xml и/или text, соответственно
• setRequestHeader(name, value) те заголовки что отходят от стандарта, заменят старое значение на новое, а не конкатенируют старое и новые значения
• getAllResponseHeaders()
• getResponseHeader()
• statusCode()
• abort()

Механизма onreadystatechange не предусмотрено, так как done, fail, always и statusCode охватывает все возможные требования.

Очередность функций обратного вызова

Все параметры beforeSend, error, dataFilter, success и complete принимают в качестве значений функции обратного вызова, которые вызываются в соотвествующие моменты времени.

С версии jQuery 1.5 функции fail и done, и, начиная с jQuery 1.6, always вызовутся в первую очередь, первыми из упрвляемой очереди, что позволяет более чем один обработчик для каждого элемента очереди. Смотрите отложенные методы, которые реализуют внутренности обработчиков метода $.ajax().

Функции обратного вызова предоставленные методом $.ajax() следующие:

1. beforeSend вызывается всегда; принимает jqXHR объект и объект settings как параметры.
2. error вызывается, если запрос выполняется с ошибкой. Принимает объект jqXHR, строку со статусом ошибки и объект исключения если применимо. Некоторые встроенные ошибки обеспечивают строку качестве объекта исключения: «abort», «timeout», «No Transport».
3. dataFilter вызывается немедленно при успешном получении данных ответа. Принимает в качестве параметров возвращенные данные и знчение параметра dataType и должен вернуть (возможно измененные данные) для передачи далее в обработчик success.
4. success вызывается если запрос выполнен успешно. Принимает данные ответа, строку содержащую код успеха и объект jqXHR.
5. Promise обработчик — .done(), .fail(), .always() и .then() — выполняются, в том порядке в котором зарегистрированы.
6. complete вызывается когда запрос закончен, независимо от успеха или неудачи выполнения запроса. Принимает объект jqXHR, отформатированную строку со статусом успеха или ошибки.

Типы данных

Различные типы ответа на вызов $.ajax() подвергаются различным видам предварительной обработки перед передачей обработчика success. Тип предварительной подготовки зависит от указанного в ответе поля заголовка Content-Type, но может быть явно указан при помощи опции dataType. Если параметр dataType задан, то поле заголовка Content-Type будет проигнорирован.

Возможны следующие типы данных: text, html, xml, json, jsonp и script.

Если указан text или html, никакой предварительной обработки не происходит. Данные просто передаются в обработчик success и доступны через свойство responseText объекта jqXHR.

Если указан xml, то ответ парсится при помощи jQuery.parseXML перед передачей в XMLDocument в обработчик success. XML документ доступен через свойство responseXML объекта jqXHR.

Если указан json, то ответ парсится при помощи jQuery.parseJSON перед передачей в объект для обработчика success. Полученный JSON объект доступен через свойство responseJSON объекта jqXHR.

Если указан script, то $.ajax() выполнит JavaScript код который будет принят от сервере перед передачей этого кода как строки в обработчик success.

Если указан jsonp, $.ajax() автоматически добавит в строку URL запроса параметр (по умолчанию) callback=?. Параметры jsonp и jsonpCallback из объекта settings переданных в метод $.ajax() могут быть использованы для указания имени URL-параметра и имени JSONP функции обратного вызова соответственно. Сервер должен вернуть корректный Javascript который будет переда в обработчик JSONP. $.ajax() выполнит возвращенный JavaScript код, вызвыв функцию JSONP по ее имени, перед передачей JSON объекта в обработчик success.

Отправка данных на сервер

По умолчанию, Ajax запросы отправляются при помощи GET HTTP метода. Если POST метод требуется, то метод следует указать в настройках при помощи параметра type. Этот параметр влияет на то как данные из параметра data будут отправлены на сервер. Данные POST запроса всегда будут переданы на сервере в UTF-8 кодировкепо стандарту W3C XMLHTTPRequest.

Параметр data может содержать строку произвольной формы, например сериализованная форма key1=value1&key2=value2 или Javascript объект {key1: 'value1', key2: 'value2'}. Если используется последний вариант, то данные будут преобразованы в строку при помощи метода jQuery.param() перед их отправкой. Эта обработка может быть отключена при помощи указания значения false в параметре processData. Обработка может быть нежелательной, если Вы хотите отправить на сервере XML документ, в этом случае измените параметр contentType с application/x-www-form-urlencoded на более подходящий MIME тип.

Расширенные настройки

Параметр global предотвращает выполнение обработчиков зарегистрированных при помощи методов .ajaxSend(), .ajaxError() и подобных методов. Это может быть полезно, например, для скрытия индикатора загрузки реализованного при помощи .ajaxSend() если запросы выполняются часто и быстро. С кросс-доменными и JSONP запросами, параметр global автоматически устанавливается в значение false.

Если сервер выполняет HTTP аутентификацию перед предоствлением ответа, то имя пользователя и пароль должны быть отправлены при помощи параметров username и password options.

Ajax запросы ограничены по времени, так что ошибки могут быть перехвачены и обработаны, чтобы обеспечить наилучшее взаимодействие с пользователем. Таймауты запроса обычно либо установлены по умолчанию, либо установлены глобально при помощи $.ajaxSetup() вместо того чтобы указывать параметр timeout для каждого отдельного запроса.

По умолчанию, запросы всегда совершаются, но браузер может предоставить ответ из своего кэша. Для запрета на использования кэшированных результатов установите значение параметра cache в false. Для того чтобы вызвать запрос с отчетом об изменении ресурса со времени последнего запроса установите значение параметра ifModified в true.

Параметр scriptCharset разрешает кодировку которая будет явно использована в запросах использующих тэг <script> (то есть тип данных script или jsonp). Это применимо в случае если удаленный скрипт и Ваша текущая страница используют разные кодировки.

Первая буква в слове Ajax означает «асинхронный», что означает что операция происходит параллельно и порядок ее выполнения не гарантируется. Параметр async метода $.ajax() по умолчанию равен true, что указывает что выполнение кода может быть продолжено после совершения запроса. Установка этого параметра в false (и следовательно, не делая Ваш вывод более асинхронным) настоятельно не рекомендуется, так как это может привести к тому что браузер перестанет отвечать на запросы.

Метод $.ajax() вернет объект XMLHttpRequest который и создает. Обычно jQuery обрабатывает создание этого объекта внутри, но можно указать при помощи параметра xhr функция которая переопределит поведение по умолчанию. Возвращаемый объект обычно может быть отброшен, но должен обеспечивать интерфейс низкого уровня для манипуляции и управления запросом. В частности, вызов .abort() на этом объекте должен будет остановить запрос до его завершения.

Расширение Ajax

Начиная с jQuery 1.5, реализация Ajax в jQuery включает предварительные фильтры, транспорты и преобразователи, которые позволят Вам очень гибко настроить Ajax запросы под любые нужды.

Использование преобразований

$.ajax() преобразователи поддерживают трансформацию одних типов данных другие. Однако, если Вы хотите трансформировать пользовательский тип данных в известный тип данных (например json), Вы должны добавить добавить соответствие между Content-Type ответа и фактическим типом данных, используя параметр contents:

    mycustomtype: /mycustomtype/
    "mycustomtype json": function( result ) {

Этот дополнительный объект необходим, потому что Content-Types ответа и типы данных никогда не имеют однозначного соответствия между собой (отсюда и регулярное выражение).

Для преобразования из поддерживаемого типа (например text или json) в пользовательский тип данных и обратно, используйте другой сквозной преобразователь:

    mycustomtype: /mycustomtype/
    "text mycustomtype": true,
    "mycustomtype json": function( result ) {

Пример выше позволяет перейти из text в mycustomtype и затем из mycustomtype в json.