javascript - Use data from two locations in Firebase, reading data simultaneously -

i want read data 2 database locations, , use these bits of data in function. way doing this:

firebase.database().ref('/data/').once('value').then(function(data1) {   firebase.database().ref('/datatwo/').once('value').then(function(data2) {        //here can use data1.val() , data2.val()     }); }); 

however, understand begins reading /otherdata after first piece of data has finished retrieving. there way simultaneously download these 2 pieces of data , use them in function 1 both complete?

thanks

use promise.all():

promise.all([   firebase.database().ref('/data/').once('value'),   firebase.database().ref('/datatwo/').once('value') ]).then(function(results) {    var data1 = results[0],        data2 = results[1];    //here can use data1.val() , data2.val() });