Simple shim for promise-nodecb interop without requiring a full-blown promise library. (Useful as a boilerplate for AWS Lambda functions.)

promise-node-shim.js

Promise.fromCallback = fn =>
    new Promise((r, j) => {
        fn((err, result) => err ? j(err) : r(result));
    });

Promise.prototype.nodeify = function (cb) {
    cb && this.then(r => cb(null, r), cb);
    return cb ? undefined : this;
};