Typescript variable inside function allocates information outside of it it is empty

Question

I need to take a variable within that function

    this.rooms.subscribe(
  function (x) {
      y= x[0].id;
      alert(y)
    });

but when access it out of function it returns to its initial value

here the whole code:

openChat(cid, nome) {
    let y = ''

    this.rooms = this.db.collection<roomMembers>
      ('room-members', ref => ref.where('uid', '==', this.uid).where('uidOutro', '==', cid)).valueChanges();

    this.rooms.subscribe(
      function (x) {
        y = x[0].id;
        alert(y)
      }
    );
    alert(y)

    this.navCtrl.push(Chat, {
      uid: cid,
      nome: nome,
      id: y
    });

  }

Answer 1

When Voce uses LET it is limiting its value to the scope where it was declared.

When Voce reuses the variable y = x[0]. id;, put this new value of y in a new scope.

To solve your problem use VAR instead of LET, or refactor the code so that the value is returned.

Answer 2

I think that function subscribe is asynchronous. This means that your alert from the outside executes before of you changing the value of y. You can only use y after having assigned a value within the callback. That is, do so:

openChat(cid, nome) {
    let y = ''

    this.rooms = this.db.collection<roomMembers> // isso é typescript?
      ('room-members', ref => ref.where('uid', '==', this.uid).where('uidOutro', '==', cid)).valueChanges();

    let contexto = this;
    this.rooms.subscribe(
      function (x) {
        y = x[0].id;
        contexto.navCtrl.push(Chat, {
          uid: cid,
          nome: nome,
          id: y
        });
      }
    );
}