fetchFavicons.js

'use strict';
 
// OMITTED: Working code
 
/** Serialize the body of a Response to a data: URI */
function responseToDataURI(response) {
    return new Promise(function(resolve, reject) {
        try {
            let reader = new FileReader();
            reader.addEventListener("load", function(e) {
                resolve(e.target.result);
            });
 
            response.blob().then((blob) => reader.readAsDataURL(blob));
        } catch (e) {
            console.log("RTDU ERR:", response.url);
            reject(e);
        }
    });
}
 
/** Replace favicon_url in a transformTabsData entry with a data: URI */
function retrieveFavicon(data) {
    return fetch(data.favicon_url, { cache: 'force-cache' })
                .then(responseToDataURI, (err) => data);
}
 
/** Call retrieveFavicon on a list with proper error handling */
function retrieveFavicons(entries) {
  const promises = entries.map(retrieveFavicon);
  return Promise.all(promises).catch((e) => {
    console.log("RFS ERR:", e);
    return entries;
  });
}
 
// OMITTED: Working code
 
/** Handler for clicks to the browser action */
function dumpTabs() {
    browser.browserAction.setIcon({path: "icons/throbber-32.gif"});
    browser.tabs.query({})
        .then(transformTabsData)
        .then(retrieveFavicons)    // It all works if this line is commented out
        .then(toJSONBlob)
        .then(function(blob) {
            browser.downloads.download({
                url: URL.createObjectURL(blob),
                filename: 'tabs.json',
                conflictAction: 'overwrite',
            })
        })
        // FIXME: Why doesn't it log and dimiss the throbber on failure?
        //        The promises API CAN'T be brain-dead enough to force
        //        me back to nesting callbacks to get "skip to end on failure"
        .catch((e) => console.log("Tab dumping failed", e))    
        .then((_) => browser.browserAction.setIcon({ path:
            browser.runtime.getManifest().browser_action.default_icon}));
}

    chrome.browserAction.onClicked.addListener(dumpTabs);