function isIframeLoaded(id) {
    var isLoaded = document.getElementById(id).contentWindow.loaded;
    if(isLoaded) {
        $("#" + id).height($("#" + id).contents().find("#main").height());
    } else {
        setTimeout(function() {
            isIframeLoaded(id);
        }, 500)
    }
}

$(document).ready(function() {
    isIframeLoaded("demo1");
    isIframeLoaded("demo2");
});