function promisify(f, manyArgs = false) {
return function (...args) {
return new Promise((resolve, reject) => {
function callback(err, ...results) {
if (err) {
reject(err);
} else {
resolve(manyArgs ? results : results[0]);
}
}
args.push(callback);
f.call(this, ...args);
});
};
}
f = promisify(f, true);
f(...).then(arrayOfResults => ..., err => ...);