any autocomplete cities samples?

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jQuery

Hello guys... i've been looking for any samples or any code that will lists all the possible cities using jquery... but i cant find a simple sample that gives this solution... i have this code that i just copied on one site

$( "#city" ).autocomplete({
			source: function( request, response ) {
				$.ajax({
					url: "http://ws.geonames.org/searchJSON",
					dataType: "jsonp",
					data: {
						featureClass: "P",
						style: "full",
						maxRows: 12,
						name_startsWith: request.term
					},
					success: function( data ) {
						response( $.map( data.geonames, function( item ) {
							return {
								label: item.name + (item.adminName1 ? ", " + item.adminName1 : "") + ", " + item.countryName,
								value: item.name
							}
						}));
					}
				});
			},
			minLength: 2,
			select: function( event, ui ) {
				log( ui.item ?
					"Selected: " + ui.item.label :
					"Nothing selected, input was " + this.value);
			},
			open: function() {
				$( this ).removeClass( "ui-corner-all" ).addClass( "ui-corner-top" );
			},
			close: function() {
				$( this ).removeClass( "ui-corner-top" ).addClass( "ui-corner-all" );
			}
		});

but when i try to run it, gives me an error saying

404 Not Found - http://mysite.com/_subfolder/undefined?query=p"

cant really solve the problem... can anyone give me an answer to my problem please... thanks in advance