jslib/lib/function/promisify.js

// cannot use fat arrow function since we don't get the arguments, then
const promisify = (fn, context = null) => function () {
    // copy passed arguments to a new array
    const args = toArray(arguments);

    return new Promise((resolve, reject) => {
        // add a callback to the arguments, which resolves the promise with the result
        args.push((err, data) => {
            if (err) {
                reject(err);
            } else {
                resolve(data);
            }
        });

        // call the original function with our callback flavoured arguments
        fn.apply(context, args);
    });
};


export default promisify;