Example of using the getDownloadURL method to check for a file's existance

getDownloadURL-example.js

// Using promise
const listRef = storage
  .ref('screenshots/abc123.png')
  .getDownloadURL()
  .then((response) => {
    // Found it. Do whatever
  })
  .catch((err) => {
    // Didn't exist... or some other error
  })

// Using async/await
const ref = storageRef.ref('screenshots/abc123.png')
try {
  await ref.getDownloadURL()
  // Do whatever
} catch(err) {
  // Doesn't exist... or potentially some other error
}