dynamically create firebase firestore ref

createRef.js

function createRef(collectionName) {
    let result = firestore;

    function addResult(_result, collDocObj) {
        let collDocKey = Object.keys(collDocObj)[0];
        let collDocVal = Object.values(collDocObj)[0];
        return _result.collection(collDocKey).doc(collDocVal);
    }

    if (arguments[1]) {
        for (let i = 0, y = arguments[1].length; i < y; i++) {
            console.log("parent " + i + ", collection: " + Object.keys(arguments[1][i]) + ", doc: " + Object.values(arguments[1][i]) + ".")
            result = addResult(result, arguments[1][i]);
        }
    }
    return result.collection(collectionName);
}

// usage
// createRef('collectionName', [{rootParentCollectionName: 'rootParentDocName'}, {secondParentCollectionName: 'secondParentDocName'}])
// result:
// firestore.collection('rootParentCollectionName').doc('rootParentDocName')
//          .collection('secondParentCollectionName').doc('secondParentDocName')
//          .collection('collectionName')

future improvement might be, to create 'docName' at the end