javascript - json last error returns 4 -

i trying send array js php through ajax call.to achieve first converted string json using json.stringify() , @ other end used json_decode() decode, didn't work out.

using json_last_error() found error 4.

js code looks this

        var form_data = $(this).serialize();          form_data+='&extraitems='+json.stringify(extraitems);         var button_content = $(this).find('button[type=submit]');          form_data=form_data+'&landtype='+landtype;         button_content.html('adding...'); //loading button text         $.ajax({ //make ajax request cart_process.php             url: "/cart/cart_process.php",             type: "post",             datatype: "json", //expect json value server             data: form_data         }).done(function (data) { //on ajax success             $("#cart-info").html(data.items); //total items in cart-info element             button_content.html('add cart'); //reset button text original text             if ($(".shopping-cart-box").css("display") == "block") { //if cart box still visible                 $(".cart-box").trigger("click"); //trigger click update cart box.             }         }) 

i appended array form data.

at php side

     foreach($_post $key => $value){         $new_product[$key] = filter_var($value, filter_sanitize_string); //create new product array     }      //we need product name , price database.       if(isset($new_product['extraitems']))     {     $newprice=0;     $extraitems=json_decode($new_product['extraitems'],true);     var_export($extraitems);     error_log(stripslashes($new_product['extraitems']));     if(is_array($extraitems))     {         foreach($extraitems $key=>$value)         {             if($value=='cherry'||$value=='chocolate chip'||$value=='butterscotch chip'||$value=='gems')                 $newprice+=50;             else if($value=='vanilla'||$value=='pineapple'||$value=='chocolate'||$value=='dark chocolate'||$value=='strawberry'||$value=='blackcurrant'||$value=='grape'||$value=='mango'||$value=='butterscotch')                 $newprice+=100;         }      }     unset($new_product['extraitems']);    } 

this snap of firebug console.

how correct problem?

update:

var_export()

'"[\\"vanilla\\",\\"chocolate\\"]"' 

the above console log shows before using json.stringify()

second 1 show after using on array.

i found solution, not working due code

 foreach($_post $key => $value){         $new_product[$key] = filter_var($value, filter_sanitize_string); //create new product array     } 

because json decode doesn't work on filter sanitized strings.