I have a JavaScript function, when I call that function it will return increment a value which is set in a PHP global variable.

Javascript calling function is : dData().

This is my Javascript function:

var dData = function() {
    alert();
};

PHP function is:

function returnincrement($a) {
    $_SESSION['UnarJ'] = $a + 1;
}

I want increment alert value should be 1,2,3,4,5,6 etc

Javascript code:

var data = {
  labels: ["12 AM","1 AM", "2 AM", "3 AM", "4 AM", "5 AM", "6 AM","7 AM", "8 AM", "9 AM", "10 AM", "11 AM"],
  datasets: [{
    fillColor: "rgba(78,156,181,.5)",
    strokeColor: "rgba(2,119,158,1)",
    data: [
    ]
  }]
};

var returndata=0;
var nextcount=0;

var dData = function() {
     $.post( "includes/hourlyud.php", function(data) {
         //var p=data;
         returndata=data;
     });
     return returndata;
};

var index = 11;
var currentampm="AM";

var ctxs = document.getElementById("cd").getContext("2d");

var barChartLine = new Chart(ctxs).Line(data, {
  responsive: true,
  barValueSpacing: 5,
  bezierCurve: false
});

var ampm = function(amorpm,cstat) {
    if (amorpm === 12 && cstat === "AM") {
        return "PM";
    }

    if (amorpm === 12 && cstat === "PM") {
        return "AM";
    }

    if (amorpm >= 1 && cstat === "AM") {
        return "AM";
    }
    else return "PM";
};

setInterval(function() {
  barChartLine.removeData();
  barChartLine.addData([dData()], index + ampm(index,currentampm));
  index++;

  if (index > 12) {
      if ((ampm(index,currentampm))==="AM") {
          currentampm="PM";
      }
      else
          currentampm="AM";

      index = 1;
  }
}, 5500);