Data HTTP request with localStorage cache (and expiry)

data.js

var data = (function () {
    var data = {};
    var mins = 5;
    var baseUrl = "http://.../api/";

    data.get = function (key, successCb, errorCb) {
        var raw = JSON.parse(localStorage.getItem(key));
        if (!raw || !raw.expiry || new Date().getTime() >= raw.expiry) {
            getFromApi(key, successCb, errorCb);
            return;
        }
        successCb(JSON.parse(raw.val));
    };

    var persist = function (key, val) {
        localStorage.setItem(key, JSON.stringify({
            val: JSON.stringify(val),
            expiry: new Date().getTime() + (mins * 60 * 1000)
        }));
    };

    var getFromApi = function (key, successCb, errorCb) {
        var uri = baseUrl + key;
        var request = new XMLHttpRequest();
        request.open("GET", uri, true);
        request.onload = function () {
            if (request.status >= 200 && request.status < 400) {
                var val = JSON.parse(request.responseText);
                persist(key, val);
                successCb(val);
            } else {
                errorCb();
            }
        };
        request.onerror = errorCb;
        request.send();
    };

    return data;
})();