function download(idx) {
    chrome.storage.local.get([`${idx}`], function(items) { // null implies all items
        // Convert object to a string.
        var result = items[`${idx}`];

        console.log(result.substr(0, 1000));

        // Save as file
        var url = 'data:text/html;base64,' + btoa(unescape(encodeURIComponent(result)));
        chrome.downloads.download({
            url: url,
            filename: `page_${idx}.html`
        });
    });
}