How can this wait until the update is finished to move to the next item?

Question

I want it to wait until .update() is done before going to the next player in the otherPlayers array. I didn't know if generators or something else could work here.

let {players} = this.props;

for(let player of otherPlayers) {
  const index = players.findIndex(p => p.Id === player.Id);
  const firebaseId = index && players[index].firebaseId;

  if(index !== -1 && firebaseId !== null) {
    window.firebase.database().ref(`/players/${firebaseId}`)
     .update({...player}, /* Callback possible */);
  } 
}

I think you can found answer in [here](http://stackoverflow.com/questions/14408718/wait-for-callback-before-continue-for-loop) . — Tan Le, Sep 12 '16 at 02:01
Do you use ES6 with babel in your code, because you could use the `await` function to make the update waiting to finish. — Sylwit, Sep 12 '16 at 02:10

Bert · Accepted Answer · 2016-09-12T02:54:33.797

Something like this possibly.

let {players} = this.props;

let p = Promise.resolve(); // just really want a promise to start

for(let player of otherPlayers) {
  const index = players.findIndex(p => p.Id === player.Id);
  const firebaseId = index && players[index].firebaseId;

  if(index !== -1 && firebaseId !== null) {
    p = p.then(()=>{
      return window.firebase.database().ref(`/players/${firebaseId}`)
       .update({...player}, /* Callback possible */);
    });
  } 
}

This starts with a resolved promise, which will cause the first update to execute immediately. Each subsequent update is chained on to the resolution of the previous promise.

How can this wait until the update is finished to move to the next item?

1 Answers1