Return best weather service that answers within a timed limit

fetchWeather.js

function fetchWeather(services, timeout) {
  let bestData = null;
  const controllers = services.map(() => new AbortController());
  const cancelFrom = index => controllers.slice(index).map(c => c.abort());
  const fetches = services.map((url, index) =>
    fetch(url, {signal: controller[index].signal})
      .then((res) => {
        bestData = res;
        cancelFrom(index+1);
        return res;
      })
  );
  const limit = new Promise(r => setTimeout(r, timeout))
    .then(() => cancelFrom(0));
  return Promise.race([limit, fetches[0]])
    .then(() => bestData)
};

You could solve it by adding a catch handler to line 6 returning the next promise in the chain - a bit ugly, but it might work!

const fetches = services.map((url, index) =>
    fetch(url, {signal: controller[index].signal})
      .then(
        res => {
          bestData = res;
          cancelFrom(index+1);
        },
        () => services[index + 1],
      )
  );