客户端JS向nodejs express服务器发送数据并响应

Question

I am trying to make an upvote and downvote system in nodejs. The client side javascript should handle the upvote and downvote functionality and send the data to the server, which will store the decisions of the user.

My question is how do I send the data to the server and how can I send back if the upvote or downvote was successfully saved?

Client side:

window.onload = function() {
  document
    .getElementsByClassName("upvote")[0]
    .addEventListener("click", function(event) {
      // tell the server that the user upvoted
    });  
};

And on the server I would do something like this I guess

app.get("/", function(req, res) {
  // save req data to a file
  if (savedToFile) {
    res.send("saved successfully");
  }
  else {
    res.send("error");
  }
});

Answer 1

I hope you are using pure javascript, then you can use Ajax to send get a request to the server like bellow inside the click event.

var xhttp = new XMLHttpRequest();
  xhttp.onreadystatechange = function() {
    if (this.readyState == 4 && this.status == 200) {
      var response = this.responseText; // here you get the response
    } 
    // handle 500 error state here
  };
  xhttp.open("GET", "server_url/upvote", true);
  xhttp.send();

After you save the data to database send the response as bellow

app.get("/upvote", function(req, res) {
  // save req data to a file
  if (savedToFile) {
    res.status(200).send("saved successfully");
  }
  else { // if got any error
    res.status(500).send("error");
  }
});