[Solved]-React Variable value is not changing-Reactjs

Your action is asynchronous. It means that 'then' function fires only when getDownloadURL() is finished. But console.log fires immidiately, when the content is null yet. So if you want to do something with content, you should do it inside 'then' callback:

let content = null;
storage.ref().child(snapshot.val().content).getDownloadURL()
.then(url => {
   content = url; 
   console.log('content', content);
} );