elm-pass/extension/portal.js

const container = document.querySelector('#app');
const app = Elm.App.embed(container);

app.ports.loadConfig.subscribe(() => {
    chrome.storage.sync.get(
        [
            'server',
            'token',
            'owner',
            'repo'
        ],
        (config) => {
            app.ports.config.send(Object.keys(config).length < 4
                                  ? null : config);
        });
});

app.ports.saveConfig.subscribe((config) => {
    chrome.storage.sync.set(config);
});