Can I have the previous ajax calling stopped when I raise a new one?

JQuery's $.ajax returns a xmlHttpRequest object which can be canceled via its native method .abort()

$("#search").autocomplete({    minLength: 3,    delay: 300, // this is in milliseconds    json: true,    source: function(request, response){        // New request 300ms after key stroke        var $this = $(this);        var $element = $(this.element);        var previous_request = $element.data( "jqXHR" );        if( previous_request ) {            // a previous request has been made.            // though we don't know if it's concluded            // we can try and kill it in case it hasn't            previous_request.abort();        }        // Store new AJAX request        $element.data( "jqXHR", $.ajax( {            type: "POST",            url: "foo.php",            dataType: "json",            success: function( data ){                response( data );            }        }));    }});

Assuming you are using jQuery UI Autocomplete:

1. You can specify the minimum length of string before starts searching. (default is 3 I guess)
2. You can also specify the delay between last keystroke and ajax call. Usually 2-300ms should do.
3. AjaxQueue might help you to clean some stuff. Dunno how (I never need it), but worth a shot :)