Check current user exists in a group using an AJAX call
$.ajax({ url: _spPageContextInfo.webAbsoluteUrl + "/_api/web/sitegroups/getByName('Site Members')/Users? $filter=Id eq " + _spPageContextInfo.userId, type: "GET", cache: true, async: false, headers:{ "ACCEPT": "application/json;odata=verbose" }, success: function (data) { if (data.d.results[0] != undefined) { //user is a member } }, error: function () { } });