I am attempting to retrieve a number of Firestore documents using data held in a string. The idea is that for each value in the array, i'd use Firestore query to retrieve the document matching that query and push it to another array. I am having a few issues achieving this. So far i've tried: 

```
exports.findMultipleItems = functions.https.onRequest((request, response) => {
    var list = ["item1", "item2", "item3", "item4"];

    var outputList = [];

    for (var i = 0; i < list.length; i++) {
        console.log("Current item: " + list[i]);
        let queryRef = db.collection("items").where('listedItems', 'array-contains', list[i]).get()
            .then(snapshot => {
                if (snapshot.empty) {
                    console.log('No matching documents.');
                }

                snapshot.forEach(doc => {
                    outputList.push(doc.data());
                });
                return;
            })
            .catch(err => {
                console.log('Error getting documents', err);
            });
    }

    response.send(JSON.stringify(outputList));

});

```

I'm not entirely sure but i think one of the issues is that the for loop is being completed before the queries have a chance to finish.

P.s - this is being ran through Cloud Functions using Admin SDK.