如何在php中清除以前的输出和回显

Question

ag.php

<?php  
ignore_user_abort(true);
set_time_limit(0);
header("Cache-Control: no-cache, must-revalidate");
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT");
$i=0;
while(1){
echo $i;
$i++;
ob_flush();
flush();

    if (connection_aborted()){
        break;
    }

    usleep(1000000);
}

ajax:

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
    console.log(xhttp.readyState+" "+xhttp.status);
  if (xhttp.readyState === 3 && xhttp.status ===200) {
      console.log(xhttp.responseText+"
");

       }
  };
  xhttp.open("GET", "ag.php", true);
  xhttp.send();

hi, at above code, i want to make a persistent connection with php and echo data in while block in 1 second interval and data comes browser like this;
0
01
012
0123
...
but i want echo data to browser like;
0
1
2
3
...
but couldn't achive it so i found this [How to clear previously echoed items in PHP about my question but not exactly what i want i think. anybody know is there any way to empty/remove previous echoed data? is it possible? help please.

Answer 1

use substr()

        var xhttp = new XMLHttpRequest();
        var lastResponse = '';
        xhttp.onreadystatechange = function() {
            //console.log(xhttp.readyState+" "+xhttp.status);
            if (xhttp.readyState === 3 && xhttp.status ===200) {

                var currentAnswer = xhttp.responseText.substr(lastResponse.length);
                lastResponse = xhttp.responseText;
                console.log(currentAnswer+"
");

            }
        };
        xhttp.open("GET", "ag.php", true);
        xhttp.send();