how to show popup message?

function OnResetClick() {
      var userEmail = document.getElementById("ContentPlaceHolder1_User");
      var val = user.value;
      var r = "";
      var getPassword = {
          type: "POST",
          url: "main.aspx/GetString",
          data: "",
          contentType: "application/json; charset=utf-8",
          dataType: "json",
          success: function (response) {
            r = response.d;
            
            GetMsg(val, r);
          },
          error: function (result) {
            alert("Error in seding mail");
          }
        };
        //Call the PageMethods
        $.ajax(getPassword);
      }

function GetMsg(val, r) {
      if (randomPassword != "") {
        var options = {
          type: "POST",
          url: "main.aspx/GeMessage",
          data: "{'toMailAddress':'" + val + "','r':'" + r + "'}",
          contentType: "application/json; charset=utf-8",
          dataType: "json",
          success: function (response) {
            var val1 = response.d;
            // some times it shows, but mostly this alart 
            // message does not comes
            alert(val1);
          },
          error: function (result) {
            alert("Error in " + result);
          }
        };
        //Call the PageMethods
        $.ajax(options);
      }
    }