Json Unexpected end of JSON input

[andreaesposito77]

Hi all,
i have this two files:

function addToCart(id){
    var xhr = new XMLHttpRequest();
    xhr.open("POST","addToCart.php");
    
    xhr.onreadystatechange= function(){
        
        
        if( this.readyState === 4){
            
            if( (this.status == 200) && (this.status < 300)){
                var resp = JSON.parse(this.responseText);
                if( resp.response === 1){
                    alert("dati inviati e memorizzati");
                    
                }else{
                    alert("dati inviati ma non memorizzati");
                }
                
            }
        }
    }
     //invio dati
    xhr.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    var product_id="product_id="+id;
    xhr.send("product_id");
}

and a php file:

<?php
header("Content-Type: application/json; charset=UTF-8");
class response_obj{
    //response=1 ok $response=0 not ok
    private $response=0;
    public function set_response($value){
         $response = $value;
     }
    public function get_response(){
	    return $response;
    }
}
function addToCart(){
	$resp = new response_obj();
	if( isset($_POST['product_id'])){
		//inserisci il prodotto nel carrello e invia dati al client
		$db= new PDO('sqlite:/home/and/Documenti/sqlite/ecomm') or die("Could not connect to the database");
		$sql = "Insert into cart (id) values (".$_POST['product_id'].")"; 
		echo $sql."\n";
		if( $db->exec($sql) == true){
			//invia risposta al client  
			$resp->set_response(1);
			//$resp->response=1;
			echo json_encode($resp);
		}
		else{//inserimento nel database non possibile avvisa l utente
			$response->set_response(0);
			//$resp->response=0;
			echo json_encode($resp);
		}
	}else{
		echo "\$_POST['product_id'] non definito\n";
	}
}

?>

every time that i execute it in the browser i receive this error:
VM84:1 Uncaught SyntaxError: Unexpected end of JSON input
at JSON.parse ()
at XMLHttpRequest.xhr.onreadystatechange (jsFunctions.js:11)
what is the problem?I think i make some errors in the php file.

[droopsnoot]

Is it because you’re echoing the contents of the query before you echo the actual output? As your javascript doesn’t skip that part, it’s trying to JSON-decode something that wasn’t encoded in the first place.

Also, in here:

    var product_id="product_id="+id;
    xhr.send("product_id");

doesn’t that mean you’re sending a string literal containing “product_id” as text, rather than sending the contents of the product_id variable that you create on the previous line? That would surely mean that your PHP code isn’t getting a product id, so it’s throwing an error message. The error message also isn’t JSON-encoded, so would cause a problem when you try to decode it.