使用Ajax调用将数据从NodeJS发送到客户端

Question

I increase a value at the server by running an Ajax call and want to update my UI after doing this

function increaseHitpoints(){
  $.ajax({
    type: 'GET',
    url: 'http://localhost:8888/incHp/2312'
  }).done(function (data) {
    $("#txtHitpoints").html(data);
  });
}

In my app.js I read a JSON file, manipulate the value, write it back to the file and return it to the client

app.get('/incHp/:id', function (req, res) {
  var database = './database.json';
  fs.readFile(database, 'utf8', function (err, data) { // read the data
      var json = JSON.parse(data);
      var users = json.users;
      var hitpoints;
      users.find(u => {
          if (u.id === Number(req.params.id)) { // get the user by id
            u.hitpoints++;
            hitpoints = u.hitpoints;
          }
      });
      json = JSON.stringify(json);
      fs.writeFile(database, json, (err) => { // update the JSON file

           // -> missing part here <-

      });
  });
});

what do I have to pass into the missing part if I want to return the new value? The new value would be hitpoints

I tried res.send(hitpoints); but it seems this function wants to return a status code, not a value.

Answer 1

If you send a numerical value, it will be observed as an HTTP response code https://expressjs.com/en/api.html#res

But you can send your hitpoints as a string res.send(hitpoints.toString()) or as json res.send({hits: hitpoints});

Answer 2

Depends on what format you want your response to be. I prefer using JSON. So in JSON case you would do this:

fs.writeFile(database, json, (err) => { 
  res.status(200).json({yourKey: yourValue});
});

Then you can access the JSON object in your frontend:

$("#txtHitpoints").html(data.yourKey);