Uncaught SyntaxError: Unexpected token u in JSON at position 0

Question

Uncaught SyntaxError: Unexpected token u in JSON at position 0

I have an array that I take from localStorage using the following code

function loadCart(data) {
//проверяю есть ли в localStorage запись cart
if (localStorage.getItem('cart')) {
    // если есть - расширфровываю и записываю в переменную cart
    cart = JSON.parse(localStorage.getItem('cart'));
        if(isEmpty(cart)){
            $('.main-cart').html('Корзина пуста');
        }
        else init();
}
else {
   $('.main-cart').html('Корзина пуста');
}

}

After that, I load an associative array with products from the database

function init(){
$.post(
 'pages/adminPage/core.php',
{
    "action":"loadGoods"
},
showCart
);
}

And I withdraw the product from localStorage

        function showCart(data) {
var pack= JSON.parse(data);

var out = '';
    for (var id in cart) {
        for (key in pack) {
            if(id===pack[key].id){
                out += `<button data-id="${id}" class="del-goods">x</button>`;
                out += `<img src="pages/orderPage/goods/${pack[key].img}" 
                width='50em' height='50em'>`;
                out += ` ${pack[key].name  }`;
                out += `  <button data-id="${id}" class="minus-goods">- 
      </button>  `;
                out += ` ${cart[id]} `;
                out += `  <button data-id="${id}" class="plus-goods">+ 
      </button>  `;
                out += cart[id]*pack[key].cost;
                out += '<br>';
            }
        }
    }
$('.main-cart').html(out);
$('.del-goods').on('click', deleteGoods);
$('.plus-goods').on('click', plusGoods);
$('.minus-goods').on('click', minusGoods);
}

The problem is that when I perform the function minusGoods

function minusGoods(){
//уменьшает товар в корзине на 1
var id = $(this).attr('data-id');
if (cart[id]===1){
    delete cart[id];
}
else cart[id]--;
saveCart();
showCart();

}

This error is thrown Uncaught SyntaxError: Unexpected token u in JSON at position 0 Most likely I'm doing it wrong, please tell me what it is problem

1

javascript localstorage

Author: Кирилл Четвертков, 2018-09-19

Source

1 answers

score 1 · Accepted Answer

showCart called without parameters, so at runtime the value of the parameter data - will be undefined.

Next is an attempt to call

data=JSON.parse(data);

Which in this case is equivalent to

data=JSON.parse(undefined);

undefined it is converted to a string "undefined" - and an attempt is made to parse this string as JSON.

As a result, a natural mistake:

try {
  JSON.parse('undefined');
} catch (e) {
  console.log(e + '');
}

To solve it, you just need to pass the parameter to the function. Based on the provided code, something like:

showCart(cart[id]);

Either check whether a parameter is passed inside the function or not:

if(!isEmpty(cart) && data){

And as an alternative-to use different functions for init and normal work.