$editor.on('input propertychange', function () {
    var outputHtml = marked($('#editor').val());
    $output.html(outputHtml);
    console.log($('#editor').val());
});

.editor {
    resize: none;
    width: 100%;
    height: 100%;
    overflow-y: auto;
    overflow-x: hidden;
}
.output {
    padding: 5px;
    padding-top: 15px;
    overflow-y: auto;
    overflow-x: hidden;
}