Values are stored as strings so on retrieval you'll need to use functions

examples/store/string.html
<!DOCTYPE html>
<html lang="en">
<head><title>String</title></head>
<body>
<script>
var a = 23;
var b = 19;
console.log(a+b);
localStorage.setItem('a', a);
console.log(localStorage.getItem('a') + b);
</script>

</body>
</html>