>>>>>Hi,
>>>>>
>>>>>Say I have the following strings (serialized JSON) (Key and Value in the local storage (simplified):
>>>>>
>>>>>

>>>>>"PM_ABCD","long string is here"
>>>>>"PM_1233", "another long string here"
>>>>>"ABC", "Another long string"
>>>>>"PM_G134555","long string"
>>>>>

>>>>>
>>>>>Can I get all keys - into an object - (without getting the Value) that start with a string "PM_"?
>>>>
>>>>As Rob says you will need to iterate localStorage:

String.prototype.startsWith = function(startText) {
>>>>        return this.slice(0, startText.length) == startText;
>>>>    };
>>>>    
>>>>    var pmKeys = new Array();
>>>>    for (var x = 1; x < localStorage.length; x++) {
>>>>        var s = localStorage.key(x);
>>>>        if (s.startsWith("PM_")) {
>>>>            pmKeys.push(s);
>>>>        }
>>>>    }

But it may be better to store all those items as an array of objects under one key.e.g:

var toStore = [
>>>>    { Key: "PM_ABCD", Value: "long string is here" },
>>>>    { Key: "PM_1233", Value: "another long string here" },
>>>>    { Key: "ABC", Value: "Another long string here" },
>>>>    { Key: "PM_G134555", Value: "long string" }
>>>>];
>>>>localStorage.setItem("MyList", JSON.stringify(toStore));

Then you can pull them back into an array which is easier to manipulate:

var myList = JSON.parse(localStorage.getItem("MyList"));
>>>>var pmKeys = new Array();
>>>>    myList.forEach(function(item) {
>>>>        if (item.Key.slice(0, 3) == "PM_") {
>>>>            pmKeys.push(item.Key);
>>>>        }
>>>>    });

I usually pull any stuff that I'm likely to need from localStorage into memory when the page loads.
>>>
>>>Thank you very much for the code and the suggestion. I will have to try the approach of array of objects. But I should be able to delete or replace any one of the "items". For example, I should be able to remove the item "PM_1233" and the value or replace the Value of this key. So I will have to learn how to do it.
>>
>>I just get the whole array into memory, modify/add/delete as required then write the whole thing back to localStorage. Don't seem to have any speed concerns...
>>
>> >Another concern I have is if there is enough capacity to store all the "data" I need to store in the localStorage. I read that local storage is limited to 5MB. I >would have to run some tests to see if this is sufficient for the customer storage.
>>
>>Quota depends on the browser (and on some the user can adjust the value). Don't know if this is up to date:http://www.sitepoint.com/html5-local-storage-revisited/
>>
>>>I want to watch (later) a pluralsight course on IndexedDB. I know nothing about it now but would like to know if this is an alternative to a local storage with >higher capacity.
>>
>>Don't know much about it either - but I think there are a couple of libraries which make for a more developer-friendly approach. This looks interesting:http://mozilla.github.io/localForage/#localforage.
>>
>>Seems it will use localStorage as a fall-back if IndexDB is not available....
>
>Since my target audience is iPad Mini (which means Safari) I quickly googled for IndexedDB and Safari on iOS and found claims that IndexedDB on iOS8 and 8.1 are buggy. This is bad.

I read a blog which claims using the same id in too separate datastores then the record in one gets deleted ;-{

> So I need to create a real case of customer data (which is not so easy) to see if localStorage is enough.

Do they need *all* of the data from the server for off-line use or could they work with a subset ?

> Another approach is to tell the customer that storing locally is not an option and store on the server. Actually I am pretty much convinced that I won't be able to deliver the program that will work in a completely disconnected fashion (that it, with no WiFi).

If you can get passed the storage problem then I'd guess that the biggest problem, if multiple users are updating data off-line, would be synchronizing back to the server.......