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.
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.
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”.
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
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:
- responseXML and/or responseText when the underlying request responded with xml and/or text, respectively
- 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:
- beforeSend callback option is invoked; it receives the jqXHR object and the settings object as parameters.
- 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».
- 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 .
- success callback option is invoked, if the request succeeds. It receives the returned data, a string containing the success code, and the jqXHR object.
- Promise callbacks — .done() , .fail() , .always() , and .then() — are invoked, in the order they are registered.
- 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.
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.
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 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
.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:
- 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.
Show a message when an Ajax request fails.