Is it possible to make such a function call?

Question

JavaScript

Hello. The idea is to execute an if loop after the request.
What is the correct way to return the test variable so that the if condition will only work after the request has been executed?

async function postData(){
  fetch('/favicon.ico?_=16505383').then(function(res){
    if(res.headers.get('Content-Type').split('/')[0]=='image'){
      var test='test1';
    }else{
      var test='test2';
    }
  }).catch((error) => {
    var test='test1';
  });
  return test;
}
if(await postData()=='online'){
  console.log('online')
}else{
  console.log('offline')
}

Answer 1

var online=(async()=>{
  if(navigator.onLine){
    var date=+new Date();
    var res=await fetch('/favicon.ico?_='+date);
    var ret=await res.headers.get('Content-Type').split('/')[0]=='image';
  }else
    ret=navigator.onLine;
  return ret;
});
if(await online()==true){
  console.log('online')
}else{
  console.log('offline')
}