Progress bar with ajax and php , for the creation of pdf - php

Question

Good Morning,
I'm trying to create a script that allows you to call a php file that will create pdf, so far so good, but I'm a little at a dead end! I would like to send to the file called the situation of how PDF files are created, or how many are missing pdf create eg 1/10, 2/10 ... 10/10 or percentage 10%, 50%. 100% ..
I have looked in various places including here, so I realized I need to use this:
var timer;
//try to delete duplications. Do a generic function that does the request to php
function makeRequest(toPHP, callback) {
var xmlhttp;
if (window.XMLHttpRequest)
{// code for IE7+, Firefox, Chrome, Opera, Safari
xmlhttp=new XMLHttpRequest();
}
else
{// code for IE6, IE5
xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
}
xmlhttp.onreadystatechange=function()
{
if (xmlhttp.readyState==4 && xmlhttp.status==200)
{
callback(xmlhttp.response);
}
}
xmlhttp.open("GET",toPHP,true);
xmlhttp.send();
}
function loop() {
var loop_index = document.getElementById("loop_nr").value;
makeRequest("server_side.php?nr="+loop_index, function(response) {
document.getElementById("sumDiv").innerHTML="Total sum = " + response;
clearInterval(timer);
});
timer=setInterval(makeRequest("getter.php", function(response) {
document.getElementById("percentageDiv").innerHTML=response;
}),1000);
}
[This is an example of a code here, not mine].
have realized that I have to have a way to get results have not only the success of the call but as it is being made.
But I can not understand how this type of code you can enter with mine.
In the php file I'm sending the information in this way:
sleep(1);
$p=(100*$contaContratos)/$NContratos;
$response = array('message' => $p);
echo json_encode($response);
Here I am using percentage, and this code is inserted into a cycle that generates the pdf.
In summary it makes the percentage of how many were created pdf.
Can you give me a hand? It is that I can not understand how to relate the two files in order to make a progress bar