var stat = "unchanged"; var mes = client_id + " " + session_state; function check_session() { var targetOrigin = "https://server.example.com"; var win = window.parent.document.getElementById("op"). contentWindow; win.postMessage( mes, targetOrigin); } function setTimer() { check_session(); timerID = setInterval("check_session()",3*1000); } window.addEventListener("message", receiveMessage, false); function receiveMessage(e) { var targetOrigin = "https://server.example.com"; if (e.origin !== targetOrigin ) {return;} stat = e.data; if stat == "changed" then take the actions below... }