Unable to get resource hash about serviceworker-webpack-plugin HOT 2 CLOSED

const swPlugin = new ServiceWorkerWebpackPlugin({
    entry: path.join(context, 'src/sw.js'),
    publicPath: '/public/',
    filename: 'sw.js',
    transformOptions: (swOption) => {
        // The list of cachable assets contains contains, for each file,
        // a hash of their content. A complete hash of that would be
        // perfect as cache name.
        // We need to add a cache of the service worker file though,
        // as that one doesn't have a content cache
        const hash = crypto.createHash('sha1');
        hash.update([
            JSON.stringify(swOption.assets),
            fs.readFileSync(path.join(context, 'src/sw.js'), 'utf8'),
            isProduction ? '1' : Math.random(),
        ].join('-'));
        return {
            isProduction,
            watch,
            assets: swOption.assets,
            buildId: `${pkg.version}-${hash.digest('hex')}`,
        };
    },
});