Browser download from fetched data

download_fetched_response.js

// Most samples used createObjectURL which gave errors suggesting no longer supported by the browser.
// This implementation encodes as a base64 string and saves as an octet-stream.
// Adapted from https://stackoverflow.com/a/38384008 and https://stackoverflow.com/a/11562550
function download(filename, arrayBuffer) {
    const element = document.createElement('a');
    const base64String = btoa(String.fromCharCode(...new Uint8Array(arrayBuffer)));
    element.setAttribute('href', 'data:application/octet-stream;base64,' + base64String);
    element.setAttribute('download', filename);
    element.style.display = 'none';
    document.body.appendChild(element);
    element.click();
    document.body.removeChild(element);
}

function fetchForDownload(url, payload, filename) {
    fetch(url, {
        method: 'POST',
        body: payload,
    }).then((response) => response.arrayBuffer())
    .then((data) => download(filename, data))
    .catch((err) => console.error(err));
}