spawn.js

'use strict';

const spawn = generatorFunction => function() {
    const gen = generatorFunction.apply(this, arguments);

    return new Promise(resolve => {

        const handle = (it) => {
            if (it.done) {
                return it.value;
            }

            return Array.isArray(it.value)
                ? Promise.all(it.value).then(cb, eb)
                : Promise.resolve(it.value).then(cb, eb);
        };

        const cb = (result) => handle(gen.next(result));
        const eb = (error)  => handle(gen.throw(error));

        resolve(cb());
    });
};

const _isGeneratorFunction = (x) => {
    return typeof x === 'function' && x.constructor.name === 'GeneratorFunction';
};

spawn.all = (obj) => {
    for (const key in obj) {
        if (_isGeneratorFunction(obj[key])) {
            obj[key] = spawn(obj[key]);
        }
    }
    return obj;
};

module.exports = spawn;