I need the recivedData variable that is declared at the beginning to store the value assigned to it in the function and show it outside the function

Question

   var recivedData;
    var obj, dbParam, xmlhttp;
    obj = { "table":"customers", "limit":100 };
    dbParam = JSON.stringify(obj);
    xmlhttp = new XMLHttpRequest();
    xmlhttp.onreadystatechange = function() {
      if (this.readyState == 4 && this.status == 200) {
        recivedData=this.responseText;    
      }
    };
    xmlhttp.onreadystatechange 
    document.getElementById("demais").innerHTML = recivedData;

xmlhttp.open("GET", "reg.php", true); xmlhttp.send(); console.log(recivedData); var datasource=recivedData;