SessionStorage cache library

cache_lib.js

var CC = CC || {};
CC.CORE = CC.CORE || {};

CC.CORE.Cache = (function () {
    var defaultCacheExpiry = 15 * 60 * 1000; // default is 15 minutes
	var aMinuteInMs = (1000 * 60);
	var anHourInMs = aMinuteInMs * 60;
	
    var getCacheObject = function () {
        // Using session storage rather than local storage as caching benefit
        // is minimal so would rather have an easy way to reset it.
        return window.sessionStorage;
    };

    var isSupportStorage = function () {
        var cacheObj = getCacheObject();
        var supportsStorage = cacheObj && JSON && typeof JSON.parse === "function" && typeof JSON.stringify === "function";
        if (supportsStorage) {
            // Check for dodgy behaviour from iOS Safari in private browsing mode
            try {
                var testKey = "candc-cache-isSupportStorage-testKey";
                cacheObj[testKey] = "1";
                cacheObj.removeItem(testKey);
                return true;
            }
            catch (ex) {
                // Private browsing mode in iOS Safari, or possible full cache
            }
        }
        CC.CORE.Log("Browser does not support caching");
        return false;
    };

    var getExpiryKey = function (key) {
        return key + "_expiry";
    };

    var isCacheExpired = function (key) {
        var cacheExpiryString = getCacheObject()[getExpiryKey(key)];
        if (typeof cacheExpiryString === "string" && cacheExpiryString.length > 0) {
            var cacheExpiryInt = parseInt(cacheExpiryString);
            if (cacheExpiryInt > (new Date()).getTime()) {
                return false;
            }
        }
        return true;
    };

    var get = function (key) {
        if (isSupportStorage()) {
            if (!isCacheExpired(key)) {
                var valueString = getCacheObject()[key];
                if (typeof valueString === "string") {
                    CC.CORE.Log("Got from cache at key: " + key);
                    if (valueString.indexOf("{") === 0 || valueString.indexOf("[") === 0) {
                        var valueObj = JSON.parse(valueString);
                        return valueObj;
                    }
                    else {
                        return valueString;
                    }
                }
            }
            else {
                // remove expired entries?
                // not required as we will almost always be refreshing the cache
                // at this time
            }
        }
        return null;
    };

    var set = function (key, valueObj, validityPeriodMs) {
        var didSetInCache = false;
        if (isSupportStorage()) {
            // Get value as a string
            var cacheValue = undefined;
            if (valueObj === null || valueObj === undefined) {
                cacheValue = null;
            }
            else if (typeof valueObj === "object") {
                cacheValue = JSON.stringify(valueObj);
            }
            else if (typeof valueObj.toString === "function") {
                cacheValue = valueObj.toString();
            }
            else {
                alert("Cannot cache type: " + typeof valueObj);
            }

            // Cache value if it is valid
            if (cacheValue !== undefined) {
                // Cache value
                getCacheObject()[key] = cacheValue;
                // Ensure valid expiry period
                if (typeof validityPeriodMs !== "number" || validityPeriodMs < 1) {
                    validityPeriodMs = defaultCacheExpiry;
                }
                // Cache expiry
                getCacheObject()[getExpiryKey(key)] = ((new Date()).getTime() + validityPeriodMs).toString();
                CC.CORE.Log("Set in cache at key: " + key);
                didSetInCache = true;
            }
        }
        return didSetInCache;
    };

    var clear = function (key) {
        var cache = getCacheObject();
        cache.removeItem(key);
        cache.removeItem(getExpiryKey(key));
    };

    return {
        Get: get,
        Set: set,
        Clear: clear,
        IsSupportStorage: isSupportStorage,
        Timeout: {
            VeryShort: (aMinuteInMs * 1),
            Default: (anHourInMs * 2),
            VeryLong: (anHourInMs * 72),
        }
    };
})();