jQuery.getJSON abstraction to cache data to localStorage with invalidation option based time

getCachedJSON.js

jQuery.extend({
    getCachedJSON: function (url, callback) {
        var cacheTimeInMs = 3600000;
        var currentTimeInMs = new Date().getTime();

        var cache = {
            data:null,
            timestamp:null
        };

        if (typeof window.localStorage[url] !== "undefined") {
            cache = JSON.parse(window.localStorage[url]);

            var validCache = (currentTimeInMs - cache.timestamp) < cacheTimeInMs;

            if (validCache) {
                callback(cache.data);
                return true;
            }
        }

        $.getJSON(url, function (data) {
            cache.data = data;
            cache.timestamp = new Date().getTime();

            window.localStorage[url] = JSON.stringify(cache);

            callback(cache.data);
        });
    }
});