如何计算localStorage中的总量和总量？

Question

This is my cart:

The issue I'm having now is, total quantity and total not adding with new value but replacing with new value, so that it shows the last value. I want to add up the value.

This is the script to add for total quantity and total subtotal in the bottom:

function calTotal(param)
       {
//this carries the latest value for quantity
           var qty = $('td.qty_'+param+' input[type=text]').val();
//this carries the latest value for subtotal
           var total = $('span.sub_total_'+param+'').text();
//this shows the values respectively in the white row below
           $('span.qty_1').text(qty);
           $('span.total').text(total);
//I'm trying to add the values in localStorage but it shows in string form.
           localStorage.quantity += parseInt(qty);
           alert(localStorage.quantity);


       }

//I'm trying to add the values in localStorage but it shows in string form.For instance when first item's quantity key in '2' it should show 2. WHen next item quantity keyed in '4' it must add prev value and new value. But it shows 24 which is string, no math performed. How to solve this, please?

           localStorage.quantity += parseInt(qty);
           alert(localStorage.quantity);

Answer 1

Local storage store keys and values, where values are also strings. If you want to operate with a numeric value you need to get it from the Local storage , parse it to integer, perform the operation and store it again:

var value = parseInt(localStorage.getItem("value"));
value += 5;
localStorage.setItem("value", value);