Transform a (err, ..., callback) based function into a Promise-based function

gistfile1.txt

function promisify(func) {
    return function(...args) {
        return new Promise(function(resolve, reject) {
            func(...args, function(err, ...rest) {
                if (err)
                    return reject(err);
                resolve(...rest);
            });
        });
    }
}

var fs = require('fs');
var popen = promisify(fs.open);
var pwrite = promisify(fs.write);
popen('./horse.js', 'w+').then(function(fd) {
    return pwrite(fd, 'hello world');
}).then(function() {
    console.log('all went smoothly');
}).catch(function(err) {
    console.error('an error occurred');
    console.error(err.tostring());
});