make a node function call with a callback awaitable

awaitable.js

function awaitable(fn) {
    return new Promise((resolve, reject) => {
        let callback = (err, data) => {
            if (err) {
                reject(err);
                return;
            }
            resolve(data);
        };
        var newArgs = Array.prototype.slice.call(arguments, 1);
        newArgs.push(callback);
        fn.apply(this, newArgs);
    });
}