localstore.js

/**
 * LocalStore is a *super* simple abstraction around localStorage for easy
 * get/set/delete. We may end up wanting something more powerful like
 * BankersBox, but for now this is much lighter weight.
 *
 * If you ever need to completely wipe LocalStore for *all* users when,
 * say, changing the format of data being cached, just bump up the "version"
 * property below.
 */
window.LocalStore = {

    // Bump up "version" any time you want to completely wipe LocalStore results.
    // This lets us expire values on all users' LocalStores when deploying
    // a new version, if necessary.
    version: 4,

    keyPrefix: "ka",

    cacheKey: function(key) {
        if (!key) {
            throw new Error("Attempting to use LocalStore without a key");
        }

        return [this.keyPrefix, this.version, key].join(":");
    },

    /**
     * Get whatever data was associated with key. Returns null if no data is
     * associated with the key, regardless of key's value (null, undefined, "monkey").
     */
    get: function(key) {
        if (!this.isEnabled()) {
            return undefined;
        }

        try {
            var data = window.localStorage[LocalStore.cacheKey(key)];
            if (data) {
                return JSON.parse(data);
            }
        } catch(e) {
            // If we had trouble retrieving, like FF's NS_FILE_CORRUPTED
        }

        return null;
    },

    /**
     * Store data associated with key in localStorage
     */
    set: function(key, data) {
        if (!this.isEnabled()) {
            throw new Error("LocalStore is not enabled");
        }
        var stringified = JSON.stringify(data),
            cacheKey = LocalStore.cacheKey(key);

        try {
            window.localStorage[cacheKey] = stringified;
        } catch (e) {
            // If we had trouble storing in localStorage, we may've run over
            // the browser's 5MB limit. This should be rare, but when hit, clear
            // everything out.
            LocalStore.clearAll();
        }
    },

    /**
     * Delete whatever data was associated with key
     */
    del: function(key) {
        if (!this.isEnabled()) {
            return;
        }
        var cacheKey = this.cacheKey(key);
        if (cacheKey in window.localStorage) {
            // IE throws when deleting a key that's not currently in
            // localStorage.
            delete window.localStorage[cacheKey];
        }
    },

    isEnabled: function() {
        var enabled, uid = String(+(new Date));
        try {
            window.sessionStorage[uid] = uid;
            enabled = (window.sessionStorage[uid] === uid);
            window.sessionStorage.removeItem(uid);
            return enabled;
        } catch (e) {
            return false;
        }
    },

    /**
     * Delete all cached objects from localStorage
     */
    clearAll: function() {
        if (!this.isEnabled()) {
            return;
        }
        try {
            var i = 0;
            while (i < localStorage.length) {
                var key = localStorage.key(i);
                if (key.indexOf(LocalStore.keyPrefix + ":") === 0) {
                    delete localStorage[key];
                } else {
                    i++;
                }
            }
        } catch(e) {
            // If we had trouble accessing .length, like FF's NS_FILE_CORRUPTED
        }
    }

};