[mycoding]

Приведу реализацию ajax в JQuery, извините что полностью, просто очень хочется понять как она у них сделана.
Обратим внимание на

function complete() {
			// Process result
			if ( s.complete ) {
				s.complete.call( callbackContext, xhr, status);
			}

			// The request was completed
			if ( s.global ) {
				trigger( "ajaxComplete", [xhr, s] );
			}

			// Handle the global AJAX counter
			if ( s.global && ! --jQuery.active ) {
				jQuery.event.trigger( "ajaxStop" );
			}
		}

Т.е. этот код запустится как только завершиться загрузка.
Можете, пожалуйста объяснить, что происходит внутри этого метода

ajax: function( origSettings ) {
		var s = jQuery.extend(true, {}, jQuery.ajaxSettings, origSettings);
		
		var jsonp, status, data,
			callbackContext = origSettings && origSettings.context || s,
			type = s.type.toUpperCase();

		// convert data if not already a string
		if ( s.data && s.processData && typeof s.data !== "string" ) {
			s.data = jQuery.param( s.data, s.traditional );
		}

		// Handle JSONP Parameter Callbacks
		if ( s.dataType === "jsonp" ) {
			if ( type === "GET" ) {
				if ( !jsre.test( s.url ) ) {
					s.url += (rquery.test( s.url ) ? "&" : "?") + (s.jsonp || "callback") + "=?";
				}
			} else if ( !s.data || !jsre.test(s.data) ) {
				s.data = (s.data ? s.data + "&" : "") + (s.jsonp || "callback") + "=?";
			}
			s.dataType = "json";
		}

		// Build temporary JSONP function
		if ( s.dataType === "json" && (s.data && jsre.test(s.data) || jsre.test(s.url)) ) {
			jsonp = s.jsonpCallback || ("jsonp" + jsc++);

			// Replace the =? sequence both in the query string and the data
			if ( s.data ) {
				s.data = (s.data + "").replace(jsre, "=" + jsonp + "$1");
			}

			s.url = s.url.replace(jsre, "=" + jsonp + "$1");

			// We need to make sure
			// that a JSONP style response is executed properly
			s.dataType = "script";

			// Handle JSONP-style loading
			window[ jsonp ] = window[ jsonp ] || function( tmp ) {
				data = tmp;
				success();
				complete();
				// Garbage collect
				window[ jsonp ] = undefined;

				try {
					delete window[ jsonp ];
				} catch(e) {}

				if ( head ) {
					head.removeChild( script );
				}
			};
		}

		if ( s.dataType === "script" && s.cache === null ) {
			s.cache = false;
		}

		if ( s.cache === false && type === "GET" ) {
			var ts = now();

			// try replacing _= if it is there
			var ret = s.url.replace(rts, "$1_=" + ts + "$2");

			// if nothing was replaced, add timestamp to the end
			s.url = ret + ((ret === s.url) ? (rquery.test(s.url) ? "&" : "?") + "_=" + ts : "");
		}

		// If data is available, append data to url for get requests
		if ( s.data && type === "GET" ) {
			s.url += (rquery.test(s.url) ? "&" : "?") + s.data;
		}

		// Watch for a new set of requests
		if ( s.global && ! jQuery.active++ ) {
			jQuery.event.trigger( "ajaxStart" );
		}

		// Matches an absolute URL, and saves the domain
		var parts = rurl.exec( s.url ),
			remote = parts && (parts[1] && parts[1] !== location.protocol || parts[2] !== location.host);

		// If we're requesting a remote document
		// and trying to load JSON or Script with a GET
		if ( s.dataType === "script" && type === "GET" && remote ) {
			var head = document.getElementsByTagName("head")[0] || document.documentElement;
			var script = document.createElement("script");
			script.src = s.url;
			if ( s.scriptCharset ) {
				script.charset = s.scriptCharset;
			}

			// Handle Script loading
			if ( !jsonp ) {
				var done = false;

				// Attach handlers for all browsers
				script.onload = script.onreadystatechange = function() {
					if ( !done && (!this.readyState ||
							this.readyState === "loaded" || this.readyState === "complete") ) {
						done = true;
						success();
						complete();

						// Handle memory leak in IE
						script.onload = script.onreadystatechange = null;
						if ( head && script.parentNode ) {
							head.removeChild( script );
						}
					}
				};
			}

			// Use insertBefore instead of appendChild  to circumvent an IE6 bug.
			// This arises when a base node is used (#2709 and #4378).
			head.insertBefore( script, head.firstChild );

			// We handle everything using the script element injection
			return undefined;
		}

		var requestDone = false;

		// Create the request object
		var xhr = s.xhr();

		if ( !xhr ) {
			return;
		}

		// Open the socket
		// Passing null username, generates a login popup on Opera (#2865)
		if ( s.username ) {
			xhr.open(type, s.url, s.async, s.username, s.password);
		} else {
			xhr.open(type, s.url, s.async);
		}

		// Need an extra try/catch for cross domain requests in Firefox 3
		try {
			// Set the correct header, if data is being sent
			if ( s.data || origSettings && origSettings.contentType ) {
				xhr.setRequestHeader("Content-Type", s.contentType);
			}

			// Set the If-Modified-Since and/or If-None-Match header, if in ifModified mode.
			if ( s.ifModified ) {
				if ( jQuery.lastModified[s.url] ) {
					xhr.setRequestHeader("If-Modified-Since", jQuery.lastModified[s.url]);
				}

				if ( jQuery.etag[s.url] ) {
					xhr.setRequestHeader("If-None-Match", jQuery.etag[s.url]);
				}
			}

			// Set header so the called script knows that it's an XMLHttpRequest
			// Only send the header if it's not a remote XHR
			if ( !remote ) {
				xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
			}

			// Set the Accepts header for the server, depending on the dataType
			xhr.setRequestHeader("Accept", s.dataType && s.accepts[ s.dataType ] ?
				s.accepts[ s.dataType ] + ", */*" :
				s.accepts._default );
		} catch(e) {}

		// Allow custom headers/mimetypes and early abort
		if ( s.beforeSend && s.beforeSend.call(callbackContext, xhr, s) === false ) {
			// Handle the global AJAX counter
			if ( s.global && ! --jQuery.active ) {
				jQuery.event.trigger( "ajaxStop" );
			}

			// close opended socket
			xhr.abort();
			return false;
		}

		if ( s.global ) {
			trigger("ajaxSend", [xhr, s]);
		}

		// Wait for a response to come back
		var onreadystatechange = xhr.onreadystatechange = function( isTimeout ) {
			// The request was aborted
			if ( !xhr || xhr.readyState === 0 || isTimeout === "abort" ) {
				// Opera doesn't call onreadystatechange before this point
				// so we simulate the call
				if ( !requestDone ) {
					complete();
				}

				requestDone = true;
				if ( xhr ) {
					xhr.onreadystatechange = jQuery.noop;
				}

			// The transfer is complete and the data is available, or the request timed out
			} else if ( !requestDone && xhr && (xhr.readyState === 4 || isTimeout === "timeout") ) {
				requestDone = true;
				xhr.onreadystatechange = jQuery.noop;

				status = isTimeout === "timeout" ?
					"timeout" :
					!jQuery.httpSuccess( xhr ) ?
						"error" :
						s.ifModified && jQuery.httpNotModified( xhr, s.url ) ?
							"notmodified" :
							"success";

				var errMsg;

				if ( status === "success" ) {
					// Watch for, and catch, XML document parse errors
					try {
						// process the data (runs the xml through httpData regardless of callback)
						data = jQuery.httpData( xhr, s.dataType, s );
					} catch(err) {
						status = "parsererror";
						errMsg = err;
					}
				}

				// Make sure that the request was successful or notmodified
				if ( status === "success" || status === "notmodified" ) {
					// JSONP handles its own success callback
					if ( !jsonp ) {
						success();
					}
				} else {
					jQuery.handleError(s, xhr, status, errMsg);
				}

				// Fire the complete handlers
				complete();

				if ( isTimeout === "timeout" ) {
					xhr.abort();
				}

				// Stop memory leaks
				if ( s.async ) {
					xhr = null;
				}
			}
		};

		// Override the abort handler, if we can (IE doesn't allow it, but that's OK)
		// Opera doesn't fire onreadystatechange at all on abort
		try {
			var oldAbort = xhr.abort;
			xhr.abort = function() {
				if ( xhr ) {
					oldAbort.call( xhr );
				}

				onreadystatechange( "abort" );
			};
		} catch(e) { }

		// Timeout checker
		if ( s.async && s.timeout > 0 ) {
			setTimeout(function() {
				// Check to see if the request is still happening
				if ( xhr && !requestDone ) {
					onreadystatechange( "timeout" );
				}
			}, s.timeout);
		}

		// Send the data
		try {
			xhr.send( type === "POST" || type === "PUT" || type === "DELETE" ? s.data : null );
		} catch(e) {
			jQuery.handleError(s, xhr, null, e);
			// Fire the complete handlers
			complete();
		}

		// firefox 1.5 doesn't fire statechange for sync requests
		if ( !s.async ) {
			onreadystatechange();
		}

		function success() {
			// If a local callback was specified, fire it and pass it the data
			if ( s.success ) {
				s.success.call( callbackContext, data, status, xhr );
			}

			// Fire the global callback
			if ( s.global ) {
				trigger( "ajaxSuccess", [xhr, s] );
			}
		}

		function complete() {
			// Process result
			if ( s.complete ) {
				s.complete.call( callbackContext, xhr, status);
			}

			// The request was completed
			if ( s.global ) {
				trigger( "ajaxComplete", [xhr, s] );
			}

			// Handle the global AJAX counter
			if ( s.global && ! --jQuery.active ) {
				jQuery.event.trigger( "ajaxStop" );
			}
		}
		
		function trigger(type, args) {
			(s.context ? jQuery(s.context) : jQuery.event).trigger(type, args);
		}

		// return XMLHttpRequest to allow aborting the request etc.
		return xhr;
	},