app.js

var TodoDispatcher = require('./dispatcher/TodoDispatcher.js');

TodoDispatcher.register((payload) => {
    console.log('callback 1 start, should take 10s');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            console.log('callback 1 done, its promise resolved', payload);
            resolve(payload);
        }, 10000);
    });
});
TodoDispatcher.register((payload) => {
    console.log('callback 2 start, should take 7s');
    return new Promise((resolve, reject) => {
        setTimeout(() => {
            // XXX want to wait for callback 1
            TodoDispatcher.waitFor([1], () => {
                console.log(`callback 2 done.
                    though my time is less than callback 1, I wait for callback 1.
                    So this message should be LATER than callback 1 done`);
                resolve(payload);
            });
        }, 7000);
    });
});

TodoDispatcher.dispatch('payload 1');