jQuery1.5开始，AJAX模块新增了三个方法。 jQuery. ajaxPrefilter， jQuery. ajaxTransport，ajaxConvert。
ajax内部的处理可分为基于XMLHttpRequest的ajax请求和基于script的jsonp跨域请求。
AJAX模块的整体架构如下：
jQuery.extend({
// Counter for holding the number of active queries
active: 0,
// Last-Modified header cache for next request
lastModified: {},
etag: {},
ajaxSettings: {
url: ajaxLocation,
type: "GET",
...
},
ajaxSetup: function( target, settings ) { ...},
ajaxPrefilter: addToPrefiltersOrTransports( prefilters ),
ajaxTransport: addToPrefiltersOrTransports( transports ),
// Main method
ajax: function( url, options ) {
...
return jqXHR;
},
getJSON: function( url, data, callback ) {
return jQuery.get( url, data, callback, "json" );
},
getScript: function( url, callback ) {
return jQuery.get( url, undefined, callback, "script" );
}
});
jQuery.each( [ "get", "post" ], function( i, method ) {
jQuery[ method ] = function( url, data, callback, type ) {
return jQuery.ajax({
...
});
};
});
ajaxPrefilter：在每个请求被发送和$.ajax()处理前，设置自定义Ajax选项或修改现有选项。
ajaxTransport：创建一个对象，用于处理Ajax数据的实际传输。它提供了两种方法，send 和 abort。
- dataType为"script"的ajaxPrefilter例子：
// Handle cache's special case and crossDomain
jQuery.ajaxPrefilter( "script", function( s ) {
if ( s.cache === undefined ) {
s.cache = false;
}
if ( s.crossDomain ) {
s.type = "GET";
}
});
- dataType为"script"的ajaxTransport例子：
// Bind script tag hack transport
jQuery.ajaxTransport( "script", function( s ) {
// This transport only deals with cross domain requests
if ( s.crossDomain ) {
var script, callback;
return {
send: function( _, complete ) {
script = jQuery("<script>").prop({
async: true,
charset: s.scriptCharset,
src: s.url
}).on(
"load error",
callback = function( evt ) {
script.remove();
callback = null;
if ( evt ) {
complete( evt.type === "error" ? 404 : 200, evt.type );
}
}
);
document.head.appendChild( script[ 0 ] );
},
abort: function() {
if ( callback ) {
callback();
}
}
};
}
});
** 最终初始化完成的prefilters：**
prefilters
** 最终初始化完成的transports：**
transports
ajax代码具体实现：
// Main method
ajax: function( url, options ) {
// If url is an object, simulate pre-1.5 signature
if ( typeof url === "object" ) {
options = url;
url = undefined;
}
// Force options to be an object
options = options || {};
var transport,
...
s = jQuery.ajaxSetup( {}, options ),
deferred = jQuery.Deferred(),
...
// Fake xhr
jqXHR = {
readyState: 0,
// Builds headers hashtable if needed
getResponseHeader: function( key ) {
...
},
// Caches the header
setRequestHeader: function( name, value ) {
...
},
...
// Cancel the request
abort: function( statusText ) {
var finalText = statusText || strAbort;
if ( transport ) {
transport.abort( finalText );
}
done( 0, finalText );
return this;
}
};
// Attach deferreds
deferred.promise( jqXHR ).complete = completeDeferred.add;
jqXHR.success = jqXHR.done;
jqXHR.error = jqXHR.fail;
s.url = ( ( url || s.url || ajaxLocation ) + "" ).replace( rhash, "" )
.replace( rprotocol, ajaxLocParts[ 1 ] + "//" );
// Alias method option to type as per ticket #12004
s.type = options.method || options.type || s.method || s.type;
// Extract dataTypes list
s.dataTypes = jQuery.trim( s.dataType || "*" ).toLowerCase().match( rnotwhite ) || [ "" ];
// Convert data if not already a string
if ( s.data && s.processData && typeof s.data !== "string" ) {
s.data = jQuery.param( s.data, s.traditional );
}
// Apply prefilters
inspectPrefiltersOrTransports( prefilters, s, options, jqXHR );
// If request was aborted inside a prefilter, stop there
if ( state === 2 ) {
return jqXHR;
}
// We can fire global events as of now if asked to
// Don't fire events if jQuery.event is undefined in an AMD-usage scenario (#15118)
fireGlobals = jQuery.event && s.global;
// Watch for a new set of requests
if ( fireGlobals && jQuery.active++ === 0 ) {
jQuery.event.trigger("ajaxStart");
}
// Uppercase the type
s.type = s.type.toUpperCase();
...
// Install callbacks on deferreds
for ( i in { success: 1, error: 1, complete: 1 } ) {
jqXHR[ i ]( s[ i ] );
}
// Get transport
transport = inspectPrefiltersOrTransports( transports, s, options, jqXHR );
// If no transport, we auto-abort
if ( !transport ) {
done( -1, "No Transport" );
} else {
jqXHR.readyState = 1;
// Send global event
if ( fireGlobals ) {
globalEventContext.trigger( "ajaxSend", [ jqXHR, s ] );
}
// Timeout
if ( s.async && s.timeout > 0 ) {
timeoutTimer = setTimeout(function() {
jqXHR.abort("timeout");
}, s.timeout );
}
try {
state = 1;
transport.send( requestHeaders, done );
} catch ( e ) {
// Propagate exception as error if not done
if ( state < 2 ) {
done( -1, e );
// Simply rethrow otherwise
} else {
throw e;
}
}
}
// Callback for when everything is done
function done( status, nativeStatusText, responses, headers ) {
}
return jqXHR;
},
