  function something()
  {
  	var x = window.localStorage.getItem('bbb'); // x = hh['bbb']

  	x = x * 1 + 1; // x = x + 1

  	window.localStorage.setItem('bbb', x); // hh['bbb'] = x

  	alert(x);
  }

function add_to_cart(id)
{
	var key = 'product_' + id
	
	var x = window.localStorage.getItem(key);
	x = x * 1 + 1;
	window.localStorage.setItem(key, x);
}

  function something()
  {
  	var x = window.localStorage.getItem('bbb'); // x = hh['bbb']

  	x = x * 1 + 1; // x = x + 1

  	window.localStorage.setItem('bbb', x); // hh['bbb'] = x

  	alert(x);
  }

function add_to_cart(id)
{
	var key = 'product_' + id

	var x = window.localStorage.getItem(key);
	x = x * 1 + 1;
	window.localStorage.setItem(key, x);
}

function cart_get_number_of_items()
{
	var cnt = 0;

	for(var i = 0; i < window.localStorage.length; i++)
	{
		var key = window.localStorage.key(i); // get key
		var value = window.localStorage.getItem(key); // get value, same as in Ruby: hh[key] = x

		if(key.indexOf('product_') == 0)
		{
			cnt = cnt + value * 1;
		}
	}

	return cnt;
}
add cart_get_number_of_items function