ERR_HTTP_HEADERS_SENT caused by response to POST request after refresh node.js Express. res.send inside fs.watch callback

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On my webpage user can enter text and press send. this causes the server to append the message to a json object stored in a file. when this file is altered it then sends the new json to the client.

app.post("/recieve",function(req,res){
  watcher = fs.watch(__dirname+"/msgs/msg.json", (eventName, filename) => {
    watcher.close();
    fs.readFile(__dirname+"/msgs/msg.json", (err,data) => {
      return res.send(data);
    });
  });
})

here is the client side

async function recieveMSG(){
  $.ajax({
    url: "recieve",
    type: "POST",
    contentType: "text; charset=utf-8"
  }).done(function(data){
    $("#msgbox").html("<br>"+data+"<br>");
    recieveMSG();
  });
}

recieveMSG();

As shown in the code above, the client sends a POST request to the server. Next after the json file is changed the server responds to the POST request with the json. I know this may be the completely wrong way to do it, but I want to know why res.send(data) is being called twice on the same res object.

It seems after the first refresh the recieve POST request just doesnot do anything

fs express node.js asynchronous
1 Answers
app.post("/recieve",async function(req,res){
  try{
  watcher.close();
  }
  catch(e){
    console.log("WatcherUndefined --first execution");
  }
  watcher = fs.watch(__dirname+"/msgs/msg.json", (eventName, filename) => {
  watcher.close();
    fs.readFile(__dirname+"/msgs/msg.json", (err,data) => {
      return res.send(data);
    });
  });
})

The problem was that the watcher wasn't getting closed after the client refreshed/disconnected. After the client refreshed the res object generated by their stale request is unusable. I believe that the watcher's callback was never redefined with the new res object (after refresh). I do not know if my assumption is correct, and would like to hear other's thoughts on this as I am new to nodejs.

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