Adding if condition in JQuery Autocomplete

I'm using JQuery Autocomplete to return X1 value

$( "#autocomplete" )
// don't navigate away from the field on tab when selecting an item
.bind( "keydown", function( event ) {
    if ( event.keyCode === $.ui.keyCode.TAB &&
        $( this ).data( "autocomplete" ).menu.active ) {
        event.preventDefault();
    }
})
.autocomplete({
    minLength: 0,
    source: function( request, response ) {
        // delegate back to autocomplete, but extract the last term
        response( $.ui.autocomplete.filter(
            X1, extractLast( request.term ) ) );
    },
    focus: function() {
        // prevent value inserted on focus
        return false;
    },
    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;
    }

});

However, I want X1 values to show only if the user start typing a text that is equal to the array below:

var stt_start = [
   "I am intrested",
   "it is",    
] 

I also added the below code to check while the user is typing if the text is equal to the array stt_start

$("#autocomplete").keyup(function(event) {
   var stt=$(this).val();
   if($.inArray(stt, stt_start) > -1){
       var found = 1;
       // show X1 values from JQuery Autocomplete
    }
});

I added the check code in different places in the JQuery Autocomplete but it didn't work !

Could anyone guide me where to add this condition so X1 values will start to appear after the user typed one of the text in stt_start.