Example localStorage decorators

storage-decorators.js

// Storage decorator base class
function StorageDecorator(storage) {
    this._storage = storage;
}
StorageDecorator.prototype.getItem = function(key) {
    return this._storage.getItem(key);
}
StorageDecorator.prototype.setItem = function(key, value) {
    return this._storage.setItem(key, value);
}
StorageDecorator.prototype.removeItem = function(key) {
    return this._storage.removeItem(key);
}
StorageDecorator.prototype.keys = function(callback) {
    return (typeof this._storage.keys === "function") ?
        this._storage.keys() :
        Object.keys(this._storage);
}

// Prefix key decorator
function PrefixStorage(storage, prefix) {
    StorageDecorator.call(this, storage);
    this._prefix = prefix || "";
}
PrefixStorage.prototype = Object.create(StorageDecorator.prototype);
PrefixStorage.prototype.getItem = function(key) {
    return this._storage.getItem(this._prefix + key);
}
PrefixStorage.prototype.setItem = function(key, value) {
    return this._storage.setItem(this._prefix + key, value);
}
PrefixStorage.prototype.removeItem = function(key) {
    return this._storage.removeItem(this._prefix + key);
}
PrefixStorage.prototype.keys = function(callback) {
    var self = this;
    return self._storage.keys().filter(function(key) {
        return key.indexOf(self._prefix) === 0;
    }).map(function(key) {
        return key.slice(self._prefix.length);
    });
}

// Auto garbage collecting decorator
function GCStorage(storage, collectFilter) {
    StorageDecorator.call(this, storage);
    this.collectFilter = collectFilter;
}
GCStorage.prototype = Object.create(StorageDecorator.prototype);
GCStorage.prototype.setItem = function(key, value, callback) {
    var self = this;
    try {
        self._storage.setItem(key, value);
    } catch (e) {
        self.gc(function(collected) {
            if (collected > 0) {
                self.setItem(key, value, callback);
            } else {
                console.warn("localStorage is full");
                callback && callback(false);
            }
        });
        return;
    }
    callback && callback(true);
}
GCStorage.prototype.gc = function(callback) {
    console.warn("garbage collecting storage");
    var self = this;
    var keys = self.keys();
    var collected = 0;
    function next() {
        if (keys.length > 0) {
            var key = keys.pop();
            self.collectFilter(key, function(canCollect) {
                if (canCollect) {
                    collected++;
                    self.removeItem(key);
                }
                next();
            });
        } else {
            callback && callback(collected);
        }
    }
    next();
}