Why doesn't Return JS work?

Question

JavaScript

Why is there no access to the variable ?

<script>

navigator.getBattery().then(function(battery) {    
  level = battery.level * 100;
  return level;
});
alert(level);

</script>

Answer 1

Because you don't know how return works and what asynchronous events are.
At the moment when you call alert, the promise has not yet been fulfilled.

Answer 2

async function getBattery() {
try {
const battery = await navigator.getBattery();
level = battery level * 100;
alert(level);
} catch (error) {
console.log(error);
};
}