Firebase run script after retrieving existing data

I have a function in js that needs to refresh after I retrieve data from Firebase. firebase.database().ref('/users/' + this.userId + '/info') .on('child_added', function(snapshot){ this.myFunction(); }.bind(this));          The problem is that the data in Firebase is very large so I don't what to run the  function lots of times.              This is how I what it to run: Retrieve ALL EXISTING data from Firebase. Run the function (once). Every time more data comes in from Firebase, run the function again.   I am guessing you want to retrieve all existing data from firebase at once  then as more data comes in listen for those data changes. If that is your  case look at the method once() in firebase