Stuck inside Promise - node.js

Question

Using native node promises. Here is my code:
(req, res) =>
requestp('https://swapi.co/api/planets')
.then((planets) => Promise.all(planets.results.map(planet => {
var residents = planet.residents.map(requestp(r))
return {
planetName: planet.name,
residents: Promise.all(residents).then((r) => r.name)
}
}))
.then((planets) => res.json(planets.map(p => {
let obj = {}
return res.json(obj[p.planetName] = p.residents);
}))))
.catch((err) => res.status(400).send(err))
I am trying to return an array of objects that look like this:
{ Alderaan: ["nameofResident1","nameofResident2"]}
I seem to be getting stuck in planet.residents.map() part of my code though.
Any help would be appreciated.

Answer 1

If you break down the inner workings to some functions, not only does it make it easier to write, it makes it easier to read
In the following, to make it executable, I called the main function doit -
I also added a requestp function, which uses fetch - so the snippet wont work unless you use a modern browser (no Internet Explorer allowed here)
run the snippet, you should see the result you are looking for
// you wont need this function
var requestp = (url) => fetch(url).then(response=>response.json());
// code starts here
var getResidentName = (url) => requestp(url).then((resident) => resident.name);
var getAllResidentNames = (residents) => Promise.all(residents.map(r => getResidentName(r)));
var processPlanet = (planet) => getAllResidentNames(planet.residents).then((residents) => ({[planet.name]: residents}));
var processPlanets = (planets) => Promise.all(planets.results.map(planet => processPlanet(planet)));
// slight change so it can run in the snippet, ignore the var doit = for your code
var doit = (req, res) =>
requestp('https://swapi.co/api/planets')
.then(processPlanets)
.catch((err) => res.status(400).send(err));
// doit and log the result as a JSON string
doit().then(result => console.log(JSON.stringify(result)));
The code you would use from above can also be written
(req, res) => {
var getResidentName = (url) => requestp(url).then((resident) => resident.name);
var getAllResidentNames = (residents) => Promise.all(residents.map(r => getResidentName(r)));
var processPlanet = (planet) => getAllResidentNames(planet.residents).then((residents) => ({[planet.name]: residents}));
var processPlanets = (planets) => Promise.all(planets.results.map(planet => processPlanet(planet)));
return requestp('https://swapi.co/api/planets')
.then(processPlanets)
.catch((err) => res.status(400).send(err));
}
That way all the "support" functions are not polluting the global namespace
After you have it working, you can, if you must, refactor the code into one monolithic block quite easily