Your PHP starts like this:

<html>
<body>

Whatever else it outputs after that, it isn't going to be valid JSON.

I did some debugging in chrome and under the network tab verified the response preview

Look at the raw preview. You seem to be looking at the rendered HTML preview.

Well after 2 hours of digging (cf Edits)

I found out following :

• In my case it's a encoding problem
• mb_detect_encoding returns probably a faulty response, some strings were probably not UTF-8
• using utf8_encode() on those string solved my problem, but see note below

Here is a recursive function that can force convert to UTF-8 all the strings contained in an array:

function utf8ize($d) {
    if (is_array($d)) {
        foreach ($d as $k => $v) {
            $d[$k] = utf8ize($v);
        }
    } else if (is_string ($d)) {
        return utf8_encode($d);
    }
    return $d;
}

Use it simply like this:

echo json_encode(utf8ize($data));

Note: utf8_encode() encodes ISO-8859-1 string to UTF-8 as per the docs so if you are unsure of the input encoding iconv() or mb_convert_encoding() may be better options as noted in comments and other solutions.

The array you show has all the properties as private. this mean that this value are not available outside their class's scope.

you can look at this SO for some suggestion

Using json_encode on objects in PHP (regardless of scope)

use the JSON_FORCE_OBJECT option of json_encode:

json_encode($status, JSON_FORCE_OBJECT);

Documentation

JSON_FORCE_OBJECT (integer) Outputs an object rather than an array when a non-associative array is used. Especially useful when the recipient of the output is expecting an object and the array is empty. Available since PHP 5.3.0.

Or, if you want to preserve your "other" arrays inside your object, don't use the previous answer, just use this:

$status = array(
                "message"=>"error",
                "club_id"=>$_club_id,
                "status"=>"1",
                "membership_info"=> new stdClass()
                );

Recommended method

json_decode ("{}") will return a stdClass per default, using the below should therefor be considered safe/portable and correct.

json_encode (new stdClass);

Your solution could work..

The documentation specifies that (object) null will result in an empty object, some might therefor say that your code is valid and that it's the method to use.

PHP: Objects - Manual

If a value of any other type is converted to an object, a new instance of the stdClass built-in class is created. If the value was NULL, the new instance will be empty.

.. but, try to keep it safe!

Though you never know when/if the above will change, so if you'd like to be 100% certain that you will always will end up with a {} in your encoded data you could use a hack such as:

$empty = json_decode ("{}");
$result = json_encode($empty); // "{}"

Even though it's tedious and ugly I do assume/hope that json_encode/json_decode is compatible with one another and always will evaluate the following to true:

$a = <something>;

$a === json_decode (json_encode ($a)); 

You really should include the actual JSON in your question; without it we are working blind, but I can guess what the problem is. You are not constructing your JSON properly when there are multiple records. When you have a single recipient, your JSON might look like this:

{"readyState":4,"responseText":"","status":200,"statusText":"OK"}

That is fine, and perfectly valid JSON – and there is no issue having an empty string as a value. The problem arises when you have more than one record, when it will append them immediately after the first:

{"readyState":4,"responseText":"","status":200,"statusText":"OK"}{"readyState":4,"responseText":"","status":200,"statusText":"OK"}

This is not valid JSON.

I suggest you accumulate your JSON responses inside the loop and then output them afterwards, in the correct format. Something like:

$jsonData = [];
foreach ($emails_room_f as $email_room_f){
    //set your content in $data as you are now, then:
    $jsonData[] = $data;
}
header("Content-Type: application/json; charset=utf-8", true);
echo json_encode($jsonData);

This way you will end up with data like this:

[
    {"readyState":4,"responseText":"","status":200,"statusText":"OK"},
    {"readyState":4,"responseText":"","status":200,"statusText":"OK"}
]

Which is valid JSON. It will also work if there is no data as it will return an empty array, which is also valid JSON.

Separately from this, I am extremely suspicious of you having a utf8ize function – that is a sign you're doing other UTF-8 stuff wrong, but that's a subject for another question.

Problem is that your output has three Objects with private and protected attributes.

See this example

<?php

class sampleClass
{
    private $hello = 25;
}


$class = new sampleClass();

echo json_encode($class);

?>

Output will be {}

In your case you have array [] of three {} objects, and they are empty because all their attributes are private or protected.

But if you will change object attributes to be public, public $hello = 25; then output will be

{"hello":25}

With that line of code

var x = <?php echo $obj ?>;

...the server application echoes back the data that was submitted to it via the "js" key. It will be client that sent it that will receive it, so if in some way it is malicious, it will be that same client dealing with the consequences.

The actual sending to the server is in fact the irrelevant part of the chain: if one has the data to submit, one can also assign it to the variable x directly without the server's interference (e.g. through browser's dev tools).

It would be a different story if in PHP you would use the data to manipulate a server database, call a service, or otherwise change the application's state, and you would not first validate that data.

As to the use of json_encode: if indeed you verify that the argument is valid JSON (by checking that the return value is not false), it will produce a valid JavaScript object literal. The known cases of incompatibility (characters U+2028 and U+2029) will not occur, as by default json_encode escapes these characters.

Try this one, it will definitely works

function utf8ize($d) {
  if (is_array($d)) {
     foreach ($d as $k => $v) {
       $d[$k] = utf8ize($v);
     }
  } else if (is_string ($d)) {
     return utf8_encode($d);
  }
   return $d;
}

and then call

echo json_encode( utf8ize( $array ) );