Typescript Promisified nodejs fs functions

promisified_node_fs.ts

// promisified fs.writeFile
export function writeFile(filename, data): Promise<void> {
    return new Promise<void>((resolve, reject) =>
        fs.writeFile(filename, data, (err) => (err) ? reject(err) : resolve())
    );
}

// promisified fs.readFile
function readFile(filename): Promise<string> {
    return new Promise<string>((resolve, reject) =>
        fs.readFile(filename, (err, data) => (err) ? reject(err) : resolve(data.toString('utf-8')))
    );
}