Concat firebase数组？

var array1 = [1, 2, 3];
var array2 = [4, 5, 6];
var concatenatedArray = array1.concat(array2);
console.log(concatenatedArray);

const functions = require('firebase-functions');

exports.concatArrays = functions.https.onRequest((req, res) => {
  var array1 = [1, 2, 3];
  var array2 = [4, 5, 6];
  var concatenatedArray = array1.concat(array2);
  res.send(concatenatedArray);
});

var database = firebase.database();
var ref = database.ref('arrays');

ref.once('value').then(function(snapshot) {
  var array1 = snapshot.child('array1').val();
  var array2 = snapshot.child('array2').val();
  var concatenatedArray = array1.concat(array2);
  console.log(concatenatedArray);
});