Make a proper JSON string without using json_encode [duplicate]

First, here is some backgroung : my current company's servers use old versions of PHP (It's not an option to upgrade it) and json functions are not supported. The company made its own framework with a dedicated function but it seems that the returned string is not always a valid JSON string. I had a parsing error on a SQL request due to indent. Here is our function :

function arrayToJSON ($array) {

    $parts = array();
    $is_list = false;
    if ( is_array($array) && !$array ) return '[]' ;

    //Find out if the given array is a numerical array
    $keys = array_keys($array);
    $max_length = count($array)-1;
    if(($keys[0] === 0) and ($keys[$max_length] === $max_length)) {//See if the first key is 0 and last key is length - 1
        $is_list = true;
        for($i=0; $i<count($keys); $i++) { //See if each key correspondes to its position
            if($i != $keys[$i]) { //A key fails at position check.
                $is_list = false; //It is an associative array.
                break;
            }
        }
    }

    foreach($array as $key=>$value) {
        if(is_array($value)) { //Custom handling for arrays
            if($is_list) $parts[] = arrayToJSON($value); /* :RECURSION: */
            else $parts[] = '"' . $key . '":' . arrayToJSON($value); /* :RECURSION: */
        } else {
            $str = '';
            if(!$is_list) $str = '"' . $key . '":';

            //Custom handling for multiple data types
            if(is_int($value) || is_float($value)){
                 $str .= $value; //Numbers
            }elseif($value === false){
                 $str .= 'false'; //The booleans
            }elseif($value === true){
                 $str .= 'true';
            }elseif(is_object($value)){
                $str .= '"' . '"';
            }else{
                 $str .= '"' . str_replace(array('\\', '"',"\r\n","\n"),array('\\\\', '\\"',' ',' '),$value) . '"'; //All other things
            }

            $parts[] = $str;
        }
    }
    $json = implode(',',$parts);

    if($is_list) return '[' . $json . ']';//Return numerical JSON
    return '{' . $json . '}';//Return associative JSON
}

Here is the parsing error.

And here is my JS quickfix to it :

version = JSON.parse(request.response.replace (/([\s]{4})|[\t]/g, `\\t`)).version;

The workaround I made is to replace multiple spaces with \t but I would like to make the function work properly. So my question is : was the parsing error due to this function or does it come from something else I may have missed ? And how could I make things go right ?