Promise Chain not waiting for promises to resolve before ending

Question

I've tried to simplify these down a bit:

      passData.savedDBGames.forEach((gameInfo) => {
        return new Promise((resolve, reject) => {
          stats.getPlayersStats(gameInfo.fixtureID).then((playerStats) => {
             playerStatsPromise.push(playerStats);
             console.info('Grab Done');
             resolve();
           });
        });
      });

      Promise.all(playerStatsPromise)
        .then(function () {
          console.info('All Done');
          app.io.emit('admin', 'Admin: done');
          resolve(passData);
        });

To my understanding Promise.all should wait until all of the promises contained in playerStatsPromise have resolved?

So why does All Done finish before Grab Done?

Your code doesn't make sense. `forEach` in particular is meant to cause side-effects, however you're returning a new Promise inside of it. — aaaaaa, Dec 15 '16 at 21:02
`data2` was from the bigger promise chain. @aaaaaa I did that to try and force a Promise to be returned, thats just me experimenting. — Jamie Hutber, Dec 15 '16 at 21:03
You should never create a `new Promise` if you use a promise inside of it, you should use those directly as return. In addition you will break your code in the case where `getPlayersStats` fails because you never handle the rejecting case of the chain your start with `getPlayersStats`. — t.niese, Dec 15 '16 at 21:11

trincot · Accepted Answer · 2016-12-15T21:05:22.627

You seem to reference an undefined variable data2 when building your array playerStatsPromise. Instead use map to build your array, since that will return the promises:

  var playerStatsPromise = passData.savedDBGames.map((gameInfo) => {
    return new Promise((resolve, reject) => {
      stats.getPlayersStats(gameInfo.fixtureID).then((playerStats) => {
         console.info('Grab Done');
         resolve();
       });
    });
  });

  Promise.all(playerStatsPromise)
    .then(function () {
      console.info('All Done');
      app.io.emit('admin', 'Admin: done');
      resolve(passData);
    });

And if this is all you do in your first code block, you could simplify to:

  var playerStatsPromise = passData.savedDBGames
      .map(gameInfo => stats.getPlayersStats(gameInfo.fixtureID));

  Promise.all(playerStatsPromise)
    .then(function () {
      console.info('All Done');
      app.io.emit('admin', 'Admin: done');
      resolve(passData);
    });

Odd... I've used maps everywhere else :) But for some reason I had a brain fart. Nice one — Jamie Hutber, Dec 15 '16 at 21:05

Promise Chain not waiting for promises to resolve before ending

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