Was supporting embedded video stopped for IE 11?

[11165]

code of page

<script src= "http://player.twitch.tv/js/embed/v1.js"></script>
<div id="twitch_embedded_player"></div>
<script type="text/javascript">
    var options = {
        width: 640,
        height: 480,
        channel: "dakotaz"
    };
    window.player = new Twitch.Player("twitch_embedded_player", options);
    player.setQuality("medium");
</script>

Problem in IE11:

failed to resolve properties promise TypeError: Object doesn’t support property or method “startsWith”

IE11 won’t support new features of js as I know. Does any solutions exist of this issue?