Why is the result undefined?

Question

JavaScript

Write a function that takes an array of promises and returns the result of the one that completed first. Moreover, if the first promise generated an error, it is necessary to return it. Moreover, the solution should not call Promise.race of the standard library.

Example:

const firstPromise = new Promise((resolve) =>
  setTimeout(() => resolve(300), 300)
);
const secondPromise = new Promise((resolve) =>
  setTimeout(() => resolve(200), 200)
);
const thirdPromise = new Promise((resolve) =>
  setTimeout(() => resolve(100), 100)
);
promiseRace([firstPromise, secondPromise, thirdPromise]); // 100

function promiseRace(promises) {
          let isResolve = false;
          [...promises].forEach((prom) =>
            prom.then((p) => {
              if (p && !isResolve) {
                isResolve = true;
                if (p instanceof Error) throw p;
                return p;
              }
            })
          );
      }

if I put console.log before return, then the console gives the correct result, and the return is undefined. I do not ask for a solution, but I want an answer to the question, why is this so?

Answer 1

Because in the above code promiseRace, there is actually no return from. In this case, you need to rewrite something like this:
https://jsfiddle.net/e6cgyt21/
here the peculiarity is used that a Promise can be executed only once and it will be executed by the first fulfilled promise from the array.