I am using jQuery ajax to send an ajax request to a php file.

$.ajax({
            url: VIP_AJAX_URL + '/add',
            data: 'slug=' + slug,
            method: 'POST',
            beforeSend: function () {
                Swal.fire({
                    title: '请稍候..',
                    html: '我们正在检查。 <br/>这个过程可能需要一些时间。',
                    allowOutsideClick: false,
                    didOpen: () => {
                        Swal.showLoading()
                    }
                })
            },
            success: function (res) {
                if (res !== 'success') {
                    Swal.fire({
                        icon: 'error',
                        title: 'Oops...',
                        html: res,
                    })
                    return;
                }

                console.log(res);
            }
        })

While this request is going on, I am printing to the screen at intervals in a php file.

echo 'abc';
sleep(5);
echo 'def';
sleep(5);
echo 'ghi';

But after all processes are completed, the ajax process is terminated. I want to get the value printed on the screen while the process is in progress.

For example, I want to get the value of 'abc' when the request is made, 'def' after 5 seconds, and 'ghi' after 10 seconds. How can I do this? I want to achieve this without using sessions, cookies or databases.