Try this:
function GetFrameData() {
var $MyFrame = $("#iframeid");
// You need to wait for the iFrame content to load first
// So, that the click events work properly
$MyFrame.load(function () {
var frameBody = $MyFrame.contents().find('body');
var inf = frameBody.find('#theid').html();
});
}
// Call the function every 5 seconds
setInterval(GetFrameData, 5000);