localStorage, limits and data expiration when limits are reached

Question

I try to store objects in localStorage but sometimes I run out of space.

When I try to store an object with localStorage but don't have enough storage - is there a way to simply delete as much local data as needed to free that space, starting the deletion from the oldest elements?

Is there an API in browsers that lets me do that?

That's not a bad question, but part of the issue with any such API is that I don't think the browsers are consistent about how they respond to the limit. I think some of them throw an error; others will pop up a dialog box asking the user if they'd like to allow more storage. — Katana314, Nov 18 '13 at 19:26
Hi, I upvoted and edited your question to ask for a solution rather than an "API". Feel free to revert if you don't like the edit but I think it clarifies things. Nice question by the way. — Benjamin Gruenbaum, Nov 18 '13 at 19:31
This is not an answer for your questions but I think it could help: http://stackoverflow.com/questions/13567509/what-happens-when-localstorage-is-full — Aguardientico, Nov 18 '13 at 19:39

Benjamin Gruenbaum · Accepted Answer · 2013-11-18T19:46:59.730

Here is a small proof of concept I just whipped up. It assumes an exception is thrown when you try to store items and have no space.

Code is annotated

var Storage = function (iden) { // a storage wrapper object
    var storage; // temp storage with variable
    if (localStorage[iden]) { // if we already did this, reuse
        storage = JSON.parse(localStorage[iden]);
    } else {
        // the queue is for the item order to find out oldest
        storage = {
            __queue: [],
            items: {}
        };
    }

    function fetch(key) {
        console.log(storage);
        return storage.items[key];
    }

    function put(key, value) {
        try {
            storage.__queue.push(key);
            storage.items[key] = value;
            localStorage[iden] = JSON.stringify(storage);
        } catch (e) { // out of space
            if (storage.__queue.length === 0) throw Exception("Too big anyway");
            var k = storage.__queue.pop();
            delete storage.items[k];
            return put(key, value); //try again after deleting
        }
    }
    return {
        put: put,
        fetch: fetch
    };
};

score 5 · Answer 2 · answered Nov 18 '13 at 20:04

Inspired by @Benjamin's awesome Proof-Of-Concept i used some of his code to come out with another solution, this function will remove the least used value. For instance you have a value like user_id you read for this value a lot of times, but if this was added first you will lose it when you run out of space.

So this solution will remove the value depending on how much they were used

var Storage = function (iden) { // a storage wrapper object
    var storage; // temp storage with variable
    if (localStorage[iden]) { // if we already did this, reuse
        storage = JSON.parse(localStorage[iden]);
    } else {
        // frequency map contains which key was hit how many times.
        storage = {
            __freq: {},
            items: {}
        };
    }

    function fetch(key) {
        storage.__freq[key]++;
        return storage.items[key];
    }

    function deleteLeastUsed(){
        var min_used = '', min_value = 0;
        var keys = Object.keys(storage._freq);

        // This will be always the first key..awesome ?
        min_used = keys.pop();
        min_value = storage.__freq[min_used];

        keys.forEach(function(key){
            if( min_value > storage.__freq[key] ){
                min_used = key;
                min_value = storage.__freq[min_used];
            }
        });

        delete storage._freq[min_used]
        delete storage.items[min_used];
    }

    function put(key, value) {
        try {
            // sets frequency to 0 if the key is over-written
            // you can use this as `touch` if you don't wanna use a value more times and wan't to free it just set it to its value
            storage.__freq[key] = 0;
            storage.items[key] = value;
            localStorage[iden] = JSON.stringify(storage);
        } catch (e) { // out of space
            if ( Object.keys(storage.__freq).length === 0) 
                throw Exception("Too big anyway");
            deleteLeastUsed();
            return put(key, value); //try again after deleting
        }
    }
    return {
        put: put,
        fetch: fetch
    };
};

Besides if your data-requirements are really high you might wanna consider switching to IndexedDB instead of localStorage. :-)

score 1 · Answer 3 · answered Nov 18 '13 at 19:45

1

I've found this in google: https://github.com/pamelafox/lscache Is a 'memcache' library for localstorage

answered Nov 18 '13 at 19:45

Aguardientico

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localStorage, limits and data expiration when limits are reached

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