function AppIdService() { initAppIdService(); } function initAppIdService() { AppIdService.prototype.getAppId = function (callback) { if (!callback || typeof callback !== 'function') { throw 'callback function required'; } makeAndGetAppId('appId', callback); }; AppIdService.prototype.getAnonymousAppId = function (callback) { if (!callback || typeof callback !== 'function') { throw 'callback function required'; } makeAndGetAppId('anonymousAppId', callback); }; function makeAndGetAppId(key, callback) { chrome.storage.local.get(key, function (obj) { if (obj && obj[key]) { callback(obj[key]); return; } var setObj = {}; setObj[key] = newGuid(); chrome.storage.local.set(setObj, function () { callback(setObj[key]); }); }); } // ref: http://stackoverflow.com/a/2117523/1090359 function newGuid() { return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) { var r = Math.random() * 16 | 0, v = c === 'x' ? r : (r & 0x3 | 0x8); return v.toString(16); }); } }