Notify when required form field is skipped

reqfield.html

<script>
    $('document').ready(
                function(){
                    $('input').on('click focus',
                        function(){
                            //sample form id in order of appearance
                            var fillable = ['fn', 'ln', 'age', 'email', 'pass', 'pass_ok'];
                            $('input').css('border', '');
                            for(var i = 0; i<=fillable.indexOf(this.id); ++i){
                                z = $('#'+fillable[i]);
                                //reset border to default
                                if(this.id === fillable[i]){
                                    $(z).css('border', '');
                                    //y.style.border = '';
                                    break;
                                }
                                if( $(z).val() === ''){
                                    //sample notification 
                                    $(z).css('border','2px solid red');
                                    //y.placeholder = y.placeholder + ' is required'; 
                                    break;
                                }
                            }
                        });
                });
</script>