How to receive a value of a variable declared inside an "await"ed method?

Question

I am trying to convert an uploaded file into a string using DOMParser. To do this, i am using two methods as follows:

method to upload a file

handleFileInput(event){
    setTimeout(async ()=>{
      if(event.target.files.item(0)!=null){
        this.uploadedFile=event.target.files.item(0);
        this.XMLAsString= await this.convertFileToString(this.uploadedFile); 
        console.log("XML as String-> ",this.XMLAsString); 
      }
    }, 3500);
  }

method to convert a file to string

convertFileToString(file):String{
    let fileInString:String=null;
    let fileReader = new FileReader();
    fileReader.onload = (event) =>{
      fileInString=fileReader.result as String
    }
    fileReader.readAsText(file);
    //console.log("XML as String inside convert method-> ",this.XMLAsString);
    if(fileInString!=null){
      return fileInString
    }
  }

But when i try print the value of XMLAsString in handleFileInput(event) (in line 6) function, it returns undefined. I understand this is happening due to the fileReader.onload but now, how do i fetch the value of fileInString in XMLAsString?

NOTE: I need to keep the setTimeOut as it is, as i need it to do some other tasks.