Javascript - pobranie pliku z backendu na front FF i przekazanie do pobrania, Chrome, Edge, Safari, IE10+

example.js

var xhr = new XMLHttpRequest();
xhr.open('POST', 'nasz-url', true);
xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');
// należy wymusić 'arraybuffer'
xhr.responseType = 'arraybuffer';
xhr.onload = onLoad;
xhr.send();

function onLoad() {
    if (this.status !== 200) {
        return;
    }

    // sciagamy nazwe pliku z nagłówków
    var filename = getFilenameFromHeaders(filename);

    // typ pliku
    var fileContentType = xhr.getResponseHeader('Content-Type');

    var blob = new Blob([this.response], {type: fileContentType});

    if (typeof window.navigator.msSaveBlob !== 'undefined') {
        // Obejscie na IE # HTML7007: One or more blob URLs were revoked by closing the blob for which
        // they were created. These URLs will no longer resolve as the data backing the URL has been freed.
        window.navigator.msSaveBlob(blob, filename);
    } else {
        var URL = window.URL || window.webkitURL;
        var downloadUrl = URL.createObjectURL(blob);

        if (filename) {
            // bedziemy używać a[download]
            var a = document.createElement("a");
            // sprawdzenie czy przeglądarka wspiera attrybut [download]
            if (typeof a.download === 'undefined') {
                window.location.open = downloadUrl;
            } else {
                a.href = downloadUrl;
                a.download = filename;
                // dodajemy niewidoczny element do body i go klikamy
                document.body.appendChild(a);
                a.click();
            }
        } else {
            window.location.open = downloadUrl;
        }

        setTimeout(function () {
            URL.revokeObjectURL(downloadUrl);
        }, 100); // cleanup
    }
}

function getFilenameFromHeaders() {
    var disposition = xhr.getResponseHeader('Content-Disposition');

    if (!disposition || disposition.indexOf('attachment') === -1) {
        return "";
    }

    var filenameRegex = /filename[^;=\n]*=((['"]).*?\2|[^;\n]*)/;
    var matches = filenameRegex.exec(disposition);
    if (matches !== null && matches[1]) {
        return matches[1].replace(/['"]/g, '');
    }

    return "";
}