send json post ajax javascript

$.ajax({
    url: 'users.php',
    dataType: 'json',
    type: 'post',
    contentType: 'application/json',
    data: JSON.stringify( { "first-name": $('#first-name').val(), "last-name": $('#last-name').val() } ),
    processData: false,
    success: function( data, textStatus, jQxhr ){
        $('#response pre').html( JSON.stringify( data ) );
    },
    error: function( jqXhr, textStatus, errorThrown ){
        console.log( errorThrown );
    }
});