index.html

<script>

const fetchVideoIds = (cb) => {
    const http = new XMLHttpRequest();
    const url = 'http://localhost/fetchIds.php';
    http.open("GET", url, true);
    http.onreadystatechange = function()
    {
        if(http.readyState == 4 && http.status == 200) {
            cb(http.responseText);
        }
    }
    http.send(null);
};

const openVideoWindow = (videoIds) => {
    const youtube = 'https://www.youtube.com/watch?v=';
    const videos = JSON.parse(videoIds) || {};

    for (let i in videos) {
        window.open(youtube + videos[i]);
    }
}

fetchVideoIds(openVideoWindow);

</script>