ARC Storage - localStorage which syncs across tabs and clears once all tabs using it are gone

arc-storage.js

// ARC Storage - localStorage which syncs across tabs and clears once all tabs using it are gone. 
// refreshing with a single tab open also wipes it
// tries awful hardto match the Storage API, but uses
var ARCStorage = (function(){

    var arcStorage = {}, arcStoreSharers = 0, didInitSync = false;

    $(window).focus(function() {
        sync();
    });

    $(window).on('beforeunload', function(){
        save();
        var currentSharers = localStorage.getItem('arc-store-shares');
        // you're the last one to disconnect, you must also clear the key
        if (currentSharers <= 1){
            localStorage.removeItem('arc-store');
            localStorage.removeItem('arc-store-shares');
        }
        else {
            localStorage.setItem('arc-store-shares', --currentSharers);
        }
        // pops alert which gives time to read debug log before the window/tab is closed
        // return "HALT FOR LOGGING";
    });

    function sync(){
        arcStorage = localStorage.getItem('arc-store');
        arcStoreSharers = localStorage.getItem('arc-store-shares');
        if (arcStoreSharers === null){
            arcStoreSharers = 0;
        }
        if (arcStorage === null){
            arcStorage = {};
            save();
        }
        else {
            arcStorage = JSON.parse(arcStorage);
        }
        if (didInitSync === false){
            localStorage.setItem('arc-store-shares', ++arcStoreSharers);
            didInitSync = true;
        }
    }

    function save(){
        localStorage.setItem('arc-store', JSON.stringify(arcStorage));
    }

    function length(){
        return Object.keys(arcStorage).length;
    }

    function key(index){
        return arcStorage[Object.keys(arcStorage)[index]];
    }

    function getItem(key){
        if (arcStorage[key] === undefined){
            return null; // i hate using null, but i'm trying to be compliant to Storage
        }
        else {
            return arcStorage[key];
        }
    }

    function setItem(key, value){
        arcStorage[key] = value;
        save();
    }

    function removeItem(key){
        delete arcStorage[key];
        save();
    }

    function clear(){
        arcStorage = {};
        save();
    }

    return {
        length : length,
        key : key,
        getItem : getItem,
        setItem : setItem,
        removeItem : removeItem,
        clear : clear
    };
});