How can I loop through a collection of data and return the entire object?

Question

I have a firestore collection, and I want to return the entire thing, however I am currently only returning one item. My intuition is that because my resolve function is in the forEach it is only returning the last item it sees, however when I move it outside of the forEach my data comes back undefined

Here is what I have written:

 componentDidMount() {
    this.getItemsPromise().then((data) => {
      this.setState({ data: data })
    });
  }

  getItemsPromise() {
    return new Promise((resolve, reject) => {
      this.cancelPromise = reject;
      const db = firebase.firestore();
      db.collection("items").get().then(function(querySnapshot) {
        querySnapshot.forEach(function(doc) {
          const data = [];
          data.push(doc.data())
          resolve(data);
        });
      });
    });
  }

Answer 1

Try this. It's better you don't use const for editable array data. and you should place resolve outside of forEach so resolve not triggered in first loop.

  getItemsPromise() {
    return new Promise((resolve, reject) => {
      this.cancelPromise = reject;
      const db = firebase.firestore();
      db.collection("items").get().then(function(querySnapshot) {
        let data = [];
        querySnapshot.forEach(function(doc) {
          data.push(doc.data());
        });
        resolve(data);
      });
    });
  }