Block scope variable gets value set in anonymous function within block but this value is not available outside the function

Question

I'm trying to update the value of start inside an anonymous function contained within the block but this does not seem to be happening.

When I declare a variable with let, I imagined that this variable would be block scoped and it's value could be updated by anonymous functions within the block.

What am I doing wrong?

function getStartTime(Id) {
  let start = '';
  let bQuery = "select StartTime from database.table where Id=?";
  dbService.executeDQuery(bQuery, Id, function (error, rs_bs) {
    if (error) {
      next(error);
      return;
    }
    
    start = JSON.stringify(rs_bs[0]["StartTime"]);
    
    console.log("start in = " + start); //shows the correct value
  });
  
  console.log("start out = " + start); //this is empty
  
  return start; //nothing returned
}