Firebase not working on script but on main html it does (Javascript)

after pasting the given data of my database, doing

firebase.initializeApp(firebaseConfig);
window.db = firebase.database().ref();
window.db.once('value', snap => data = snap.val());
console.log(data);

retrieves correctly the data and its shown as i want, but making a function on a index.js

function extend(){
  window.db.once('value', snap => data = snap.val());
  console.log(data);
}
extend();

gives me this error Uncaught ReferenceError: data is not defined at extend (index.js:59) at index.js:61

I dont get why it would work outside the function and not inside, given that window.db is a global instance, i’ve tried a couple of ways differently without success, would somebody help me? 🙂

Answer

The variable data is not defined in the extend() function (unless it’s some global variable, extend()). You’ll get better results if you refactor your code like so:

// Define the local variable
function extend(){
   window.db.once('value', snap => {
      let data = snap.val();
      console.log(data);
   });
}
extend();