service.php

<?php
// cannot check for session because requests to service.php are executed from unauthenticated uses
require 'DBInfo.php';
// $returnArray = array('username' => false, 'email' => false);

if (isset($_POST['username'])){
  // echo "Received";
  $query = $link->prepare("SELECT username FROM users where username=?");
  $query->bind_param("s", $_POST['username']);
}
else if (isset($_POST['email'])){
  // echo "Received";
  $query = $link->prepare("SELECT email FROM users where  email= ? ");
  $query->bind_param("s", $_POST['email']);
}
else echo "Bad request";

if (!$query->execute())
{
  echo "Database access failed miserably".mysqli_error($link);
}
else
{
  $query->store_result();
  $numRows =  $query->num_rows();
  if (isset($_POST['username']) && $numRows == 1){
    echo json_encode(array("username"=>"taken"));
  }
    // $returnArray['username'] = true;
  else if (isset($_POST['email']) && $numRows == 1){
    echo json_encode(array("email"=>"taken"));
  }
    // $returnArray['email'] = true;
  else echo "Username or email not taken";
}