just for a reformation of code

test.js

$(function() {
	function split( val ) {
		//alert(val);
		return val.split( /,\s*/ );
	}
	function extractLast( term ) {
		return split( term ).pop();
	}

	$("#S1")
	// don't navigate away from the field on tab when selecting an item
	.bind( "keydown", function( event ) {
		if ( event.keyCode === $.ui.keyCode.TAB &&
			$( this ).autocomplete( "instance" ).menu.active ) {
			event.preventDefault();
		}
	})
	.autocomplete({
		source: function( request, response ) {
			$.getJSON( "XXX.PHP", {
				searchTerm: extractLast( request.term )
			}, response );
			//alert(response);
		},
		search: function() {
			// custom minLength
			var term = extractLast( this.value );
			if ( term.length < 1 ) {
				return false;
			}
		},
		focus: function() {
			// prevent value inserted on focus
			return false;
		},
		formatItem: function(row) {
			return "<div style='height:12px'><div style='float:left'>" + //row[0] +
				"</div>" +
				// row[1] + "/" + 
				"" + row[2] +"</div>";
		},
		select: function( event, ui ) {
			var terms = split( this.value );
			// remove the current input
			terms.pop();
			// add the selected item
			terms.push( ui.item.value );
			// add placeholder to get the comma-and-space at the end
			terms.push( "" );
			this.value = terms.join( ", " );
			return false;
		}
	});
});