jQuery.ajaxTransport()


jQuery.ajaxTransport( dataType, handler(options, originalOptions, jqXHR) )Returns: undefined

Description: Creates an object that handles the actual transmission of Ajax data.

A transport is an object that provides two methods, send and abort, that are used internally by $.ajax() to issue requests. A transport is the most advanced way to enhance $.ajax() and should be used only as a last resort when prefilters and converters are insufficient.

Since each request requires its own transport object instance, transports cannot be registered directly. Therefore, you should provide a function that returns a transport instead.

Transports factories are registered using $.ajaxTransport(). A typical registration looks like this:

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$.ajaxTransport(function( options, originalOptions, jqXHR ) {
if( /* transportCanHandleRequest */ ) {
return {
send: function( headers, completeCallback ) {
// Send code
},
abort: function() {
// Abort code
}
};
}
});

where:

  • options are the request options
  • originalOptions are the options as provided to the ajax method, unmodified and, thus, without defaults from ajaxSettings
  • jqXHR is the jqXHR object of the request
  • headers is an object of (key-value) request headers that the transport can transmit if it supports it
  • completeCallback is the callback used to notify ajax of the completion of the request

completeCallback has the following signature:

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function( status, statusText, responses, headers ) {}

where:

  • status is the HTTP status code of the response, like 200 for a typical success, or 404 for when the resource is not found.
  • statusText is the statusText of the response.
  • responses (Optional) is An object containing dataType/value that contains the response in all the formats the transport could provide (for instance, a native XMLHttpRequest object would set reponses to { xml: XMLData, text: textData } for a response that is an XML document)
  • headers (Optional) is a string containing all the response headers if the transport has access to them (akin to what XMLHttpRequest.getAllResponseHeaders() would provide).

Just like prefilters, a transport's factory function can be attached to a specific dataType:

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$.ajaxTransport( "script", function( options, originalOptions, jqXHR ) {
// Will only be called for script requests
});

The following example shows how a minimal image transport could be implemented:

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$.ajaxTransport( "image", function( s ) {
if ( s.type === "GET" && s.async ) {
var image;
return {
send: function( _ , callback ) {
image = new Image();
function done( status ) {
if ( image ) {
var statusText = ( status === 200 ) ? "success" : "error",
tmp = image;
image = image.onreadystatechange = image.onerror = image.onload = null;
callback( status, statusText, { image: tmp } );
}
}
image.onreadystatechange = image.onload = function() {
done( 200 );
};
image.onerror = function() {
done( 404 );
};
image.src = s.url;
},
abort: function() {
if ( image ) {
image = image.onreadystatechange = image.onerror = image.onload = null;
}
}
};
}
});

Handling Custom Data Types

The jQuery Ajax implementation comes with a set of standard dataTypes, such as text, json, xml, and html.

Use the converters option in $.ajaxSetup() to augment or modify the data type conversion strategies used by $.ajax().

The unminified jQuery source itself includes a list of default converters, which effectively illustrates how they can be used:

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// List of data converters
// 1) Key format is "source_type destination_type"
// (a single space in-between)
// 2) The catchall symbol "*" can be used for source_type
converters: {
// Convert anything to text
"* text": window.String,
// Text to html (true = no transformation)
"text html": true,
// Evaluate text as a json expression
"text json": jQuery.parseJSON,
// Parse text as xml
"text xml": jQuery.parseXML
}

When you specify a converters option globally in $.ajaxSetup() or per call in $.ajax(), the object will map onto the default converters, overwriting those you specify and leaving the others intact.

For example, the jQuery source uses $.ajaxSetup() to add a converter for "text script":

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jQuery.ajaxSetup({
accepts: {
script: "text/javascript, application/javascript"
},
contents: {
script: /javascript/
},
converters: {
"text script": jQuery.globalEval
}
});