<!DOCTYPE html>
<script>
function fetch_url(url) {
    return new Promise(function(resolve, reject) {
        var request = new XMLHttpRequest();
        request.addEventListener('load', function(event) {
            if (request.status == 200)
                resolve(request.response);
            else
                reject(Error(request.statusText));
        });
        request.open('GET', url);
        request.send();
    });
}
</script>