nancy[async].js

class Nancy {
    constructor(executor) {
        ...
        const laterCalls = [];
        const callLater = getMember => callback => new Nancy(resolve => laterCalls.push(() => resolve(getMember()(callback))));
        const members = {
            ...
            [states.pending]: {
                ...
                then: callLater(() => this.then),
                catch: callLater(() => this.catch)
            }
        };
        ...
        const apply = (value, state) => {
            if (this.state === states.pending) {
            ...
                for (const laterCall of laterCalls) {
                    laterCall();
                }
            }
        };
        ...
    }
    ...
}