Unexpected < token in JSON at position 0 - php

Question

I keep receiving this JSON error,i think it has something to do with html tags or any other tags that conflicts with it.
Here is my PHP Code:
<?php
require_once("connection.php");
class AddAdminUPController extends Connection{
public function addAdminUP(){
include "function.php";
$username = cleanData($_POST['username']);
$password = cleanData($_POST['password']);
if (!empty($username)){
if(!empty($password)){
if(strlen($password) > 8){
$select_query = "select * from sample_user where user_name = ?";
$stmt = $this->db->prepare($select_query);
$stmt->bindParam(1,$username);
if($stmt->execute()){
if($stmt->rowCount() <= 0){
$password = password_hash($password,PASSWORD_BCRYPT,array('cost' => 12));
$create_query = "insert into sample_user(user_name,password)values(?,?)";
$stmt = $this->db->prepare($create_query);
$stmt->bindParam(1,$username);
$stmt->bindParam(2,$password);
if($stmt->execute()){
echo "<script>".
"Materialize.toast('Created SuccessFully!', 5000, 'green')"
."</script>";
echo "<script>".
"$('#add_admin_up_form').hide();".
"$('#add_admin_up').hide();";
?>
$(".enrollment_title").html("<i class='material-icons'>fingerprint</i> Enroll Fingerprint");
<?php
echo "</script>";
include 'flexcode_sdk/include/global.php';
include 'flexcode_sdk/include/function.php';
if(isset($_GET['action']) && $_GET['action'] == 'add'){
$lastID = $this->db->lastInsertId();
?>
<script type="text/javascript">
$('title').html('User');
function user_register(user_id, user_name) {
$('body').ajaxMask();
regStats = 0;
regCt = -1;
try
{
timer_register.stop();
}
catch(err)
{
console.log('Registration timer has been init');
}
var limit = 4;
var ct = 1;
var timeout = 5000;
timer_register = $.timer(timeout, function() {
console.log("'"+user_name+"' registration checking...");
user_checkregister(user_id,$("#user_finger_"+user_id).html());
if (ct>=limit || regStats==1)
{
timer_register.stop();
console.log("'"+user_name+"' registration checking end");
if (ct>=limit && regStats==0)
{
alert("'"+user_name+"' registration fail!");
$('body').ajaxMask({ stop: true });
}
if (regStats==1)
{
$("#user_finger_"+user_id).html(regCt);
alert("'"+user_name+"' registration success!");
$('body').ajaxMask({ stop: true });
load('view_admin.php?action=add');
}
}
ct++;
});
}
function user_checkregister(user_id, current) {
$.ajax({
url : "view_admin.php?action=checkreg&user_id="+user_id+"&current="+current,
type : "GET",
success : function(data)
{
try
{
var res = jQuery.parseJSON(data);
if (res.result)
{
regStats = 1;
$.each(res, function(key, value){
if (key=='current')
{
regCt = value;
}
});
}
}
catch(err)
{
alert(err.message);
}
}
});
}
</script>
<?php
$last_id_query = "select * from sample_user where user_id = ?";
$stmt = $this->db->prepare($last_id_query);
$stmt->bindParam(1,$lastID);
if ($stmt->execute()){
while($row = $stmt->fetch(PDO::FETCH_OBJ)){
$url_register =
base64_encode($base_path."register.php?user_id=".$row->user_id);
echo "<br><a href='finspot:FingerspotReg;$url_register' onclick=\"user_register('".$row->user_id."','".$row->user_name."')\" class='fw_button general_button btn waves-effect waves-light'>Register Fingerprint</a>";
}
}
}
elseif (isset ($_GET['action']) && $_GET['action'] == 'checkreg') {
$sql1 = "SELECT count(finger_id) as ct FROM sample_finger WHERE user_id=".$_GET['user_id'];
$result1 = mysql_query($sql1);
$data1 = mysql_fetch_array($result1);
if (intval($data1['ct']) > intval($_GET['current'])) {
$res['result'] = true;
$res['current'] = intval($data1['ct']);
}
else
{
$res['result'] = false;
}
echo json_encode($res);
}
else { echo "Parameter invalid..";}
}
else{
echo "<script>".
"Materialize.toast('Query Failed!', 5000, 'red')"
."</script>";
}
}
else{
echo "<script>".
"Materialize.toast('Username already exists!', 5000, 'red')"
."</script>";
}
}
else{
echo "<script>".
"Materialize.toast('Query Failed!', 5000, 'red')"
."</script>";
}
}
else{
echo "<script>".
"Materialize.toast('Password is too short!', 5000, 'red')"
."</script>";
}
}
else{
echo "<script>".
"Materialize.toast('Password is empty!', 5000, 'red')"
."</script>";
}
}
else{
echo "<script>".
"Materialize.toast('Username is empty!', 5000, 'red')"
."</script>";
}
}
}
$add_admin_up_controller = new AddAdminUPController;
echo $add_admin_up_controller->addAdminUP();
?>
I need help in fixing this kind of error. It keeps displaying:
SyntaxError: Unexpected token < in JSON at position 0 at JSON.parse () at Function.jQuery.parseJSON (jquery.js:8520) at Object.success (eval at (jquery.js:339), :55:90) at fire (jquery.js:3148) at Object.fireWith [as resolveWith] (jquery.js:3260) at done (jquery.js:9314) at XMLHttpRequest.callback (jquery.js:9718)

Answer 1

You are returning plain text instead of JSON. In your ajax call put the response dataType: 'json' and the part of PHP:
header("Content-Type: application/json");
echo json_encode($res);
exit;

Answer 2

This error due to your responce is not in json format and your ajax request is expecting json responce .
You can change responce header by use dataType : 'text/html' in your ajax request.
Here in action .
function user_checkregister(user_id, current) {
$.ajax({
url : "view_admin.php?action=checkreg&user_id="+user_id+"&current="+current,
type : "GET",
dataType: 'text/html',
success : function(data)
{
try
{
var res = jQuery.parseJSON(data);
if (res.result)
{
regStats = 1;
$.each(res, function(key, value){
if (key=='current')
{
regCt = value;
}
});
}
}
catch(err)
{
alert(err.message);
}
}
});
}