如何检查我的XMLHttpRequest发布方法是否成功？

Question

I am not very much used to with API's. I have written one function in which I am sending data to API. I have called this function on a textbox text change event. I am not getting whether it is working or not because I am not getting any error. Below is the function:

function sendAPIData(url,introduction,coordinateid){
    var xhttp = new XMLHttpRequest();
    xhttp.open("POST", "http://192.168.51.212:3368/casigo/sDAGinput",true);
    xhttp.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
    var input = JSON.stringify({
      "coordinate": coordinateid,
      "url": url,
      "introduction": introduction
    });
    xhttp.send(input);
}

It should return me some input string.

Answer 1

To check the server's response a callback function can be used:

function sendAPIData(url,introduction,coordinateid) {
    var xhttp = new XMLHttpRequest();
    xhttp.open("POST", "http://192.168.51.212:3368/casigo/sDAGinput",true);
    xhttp.setRequestHeader("Content-Type", "application/json;charset=UTF-8");
    var input = JSON.stringify({
      "coordinate": coordinateid,
      "url": url,
      "introduction": introduction
    });

    // callback function
    xhttp.onload = function(res) {
      if (xhttp.readyState === 4) {
        if (xhttp.status === 200) {
          console.log("OK");
        } else {
          console.error("ERROR");
        }
      }
    };

    xhttp.send(input);
}

xhttp.onload is a function that will be called once the XMLHttpRequest is completed. Its argument res is the server's response.

Answer 2

XMLHttpRequest contains status and readyState properties which can be used by using the onreadystatechange event. Something like the below code should work.

xhttp.onreadystatechange=function(){
   //readyState == 4 means the request is done and a response is received from the server

   if (xhttp.readyState==4 && xhttp.status==200 && typeof(xhttp.responseText) == 'string'){
      //Do something          
   }
}