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var oldCallbacks = [],
	rquestion = /\?/,
	rjsonp = /(=)\?(?=&|$)|\?\?/,
	nonce = jQuery.now();

// Default jsonp settings
jQuery.ajaxSetup({
	jsonp: "callback",
	jsonpCallback: function() {
		var callback = oldCallbacks.pop() || ( jQuery.expando + "_" + ( nonce++ ) );
		this[ callback ] = true;
		return callback;
	}
});

// Detect, normalize options and install callbacks for jsonp requests
jQuery.ajaxPrefilter( "json jsonp", function( s, originalSettings, jqXHR ) {

	var callbackName, overwritten, responseContainer,
		data = s.data,
		url = s.url,
		hasCallback = s.jsonp !== false,
		replaceInUrl = hasCallback && rjsonp.test( url ),
		replaceInData = hasCallback && !replaceInUrl && typeof data === "string" &&
			!( s.contentType || "" ).indexOf("application/x-www-form-urlencoded") &&
			rjsonp.test( data );

	// Handle iff the expected data type is "jsonp" or we have a parameter to set
	if ( s.dataTypes[ 0 ] === "jsonp" || replaceInUrl || replaceInData ) {

		// Get callback name, remembering preexisting value associated with it
		callbackName = s.jsonpCallback = jQuery.isFunction( s.jsonpCallback ) ?
			s.jsonpCallback() :
			s.jsonpCallback;
		overwritten = window[ callbackName ];

		// Insert callback into url or form data
		if ( replaceInUrl ) {
			s.url = url.replace( rjsonp, "$1" + callbackName );
		} else if ( replaceInData ) {
			s.data = data.replace( rjsonp, "$1" + callbackName );
		} else if ( hasCallback ) {
			s.url += ( rquestion.test( url ) ? "&" : "?" ) + s.jsonp + "=" + callbackName;
		}

		// Use data converter to retrieve json after script execution
		s.converters["script json"] = function() {
			if ( !responseContainer ) {
				jQuery.error( callbackName + " was not called" );
			}
			return responseContainer[ 0 ];
		};

		// force json dataType
		s.dataTypes[ 0 ] = "json";

		// Install callback
		window[ callbackName ] = function() {
			responseContainer = arguments;
		};

		// Clean-up function (fires after converters)
		jqXHR.always(function() {
			// Restore preexisting value
			window[ callbackName ] = overwritten;

			// Save back as free
			if ( s[ callbackName ] ) {
				// make sure that re-using the options doesn't screw things around
				s.jsonpCallback = originalSettings.jsonpCallback;

				// save the callback name for future use
				oldCallbacks.push( callbackName );
			}

			// Call if it was a function and we have a response
			if ( responseContainer && jQuery.isFunction( overwritten ) ) {
				overwritten( responseContainer[ 0 ] );
			}

			responseContainer = overwritten = undefined;
		});

		// Delegate to script
		return "script";
	}
});
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