Can't use this to point a selected element with jQuery

Why this JS does not apply my class to the element please ?

<input type="password" name="customer-new-password" class="form-control">

<script>
if($("input[name='customer-new-password']").val()=='') {
    $(this).addClass('required');
}
else {
    $(this).removeClass('required');
}
</script>

Thanks.