How?

Question

How use localStorage.setItem and localStrage.getItem with JS, because he added numbers and not chars

Answer 1

if (typeof(Storage) === 'undefined') {
/*browser does not support localstorage*/
} else {
/* storage code goes here */
}

localStorage.setItem(key, value);
Sets a value to a key.

localStorage.getItem(key);
Returns a key's value

localStorage.clear();
Clears the storage

Local storage can only use strings.
Convert your variables to string when setting them
and convert them back when accessing