Javascript: call a blocking HTTP POST

Question

I have a caller function that invokes another function that send a HTTP POST with parameters. Now i want that this called function blocks execution until there is its "success" (so when its HTTP POST has been done).

This is my logical code:

var fingerprint = null;
var janus_session = null;
var inserted = "false";

$(document).ready(function() {
      //stuff
      fingerprint = FindFingerprint(jsep);

      janus_session = janus.getSessionId();
      inserted = SendSDPLine(fingerprint, janus_session);
      console.log("**in MAIN: inserted= " + inserted);

      //other stuff
    }

function SendSDPLine(fingerprint, janus_session) {
  var sdp = fingerprint;
  //    var url = "http://localhost:8484/Shine/AccountController";
  var action_type = "InsertSDPLine";
  var sessionid = janus_session;

  $.ajax({
    type: "POST",
    url: url,
    xhrFields: {
      withCredentials: false
    },
    data: {
      "action": action_type,
      "sdpline": fingerprint,
      "sessionid": sessionid
    },
    success: function(data) {
      if (data == "INSERTED") {
        inserted = "true";
        console.log("in SENDSDPLINE: inserted= " + inserted);
      }
      return inserted;
      //        return checkFingerprint (fingerprint);
    },
    // vvv---- This is the new bit
    error: function(jqXHR, textStatus, errorThrown) {
      console.log("Error, status = " + textStatus + ", " +
                  "error thrown: " + errorThrown);
    }
  });

}

In few words, i want that other stuff has been executed after that HTTP POST response has been checked. I've already seen another problem: initially, inserted has false value. In success(data) in HTTP POST response, it has true value. But, in the caller function, in the following console.log has undefined value.

So, i have two question:

how to return this value to the caller function
how to stop execution of the caller function until HTTP POST response has been received?

Maybe async/await can help you here. But if not, then it's impossible (to stop execution of the caller function) and you have to resort to using promises or callbacks. — Sergio Tulentsev, Apr 20 '17 at 08:38

score 2 · Accepted Answer · answered Apr 20 '17 at 08:46

2

If you need to block the execution until AJAX returns, you can specify async:false in ajax parameters, as per jQuery documentation.

answered Apr 20 '17 at 08:46

Sergey Kudriavtsev

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score 0 · Answer 2 · answered Apr 20 '17 at 08:43

Use callback function

var fingerprint = null;
var janus_session = null;
var inserted = "false";


$(document).ready(function() {

//stuff

fingerprint = FindFingerprint(jsep); 


janus_session = janus.getSessionId();

//Use callback funcion to access 
SendSDPLine(fingerprint,janus_session , function(error,inserted){

  if(error){
     console.log("**Error in : "+error);
  }

  console.log("**in MAIN: inserted= "+inserted);


});


//other stuff

}

function SendSDPLine(fingerprint,janus_session, callback){

  var sdp=fingerprint;
//    var url = "http://localhost:8484/Shine/AccountController";
var action_type = "InsertSDPLine";
var sessionid = janus_session;

$.ajax({
  type:    "POST",
  url:     url,
  async: false, 
  xhrFields: {
    withCredentials: false
  },
  data:{
    "action"      : action_type,
    "sdpline"     : fingerprint,
    "sessionid"   : sessionid
  },
  success: function(data) {
    if (data == "INSERTED") {
      inserted = "true";
      console.log("in SENDSDPLINE: inserted= "+inserted);

      //return result
      return callback(null, inserted);
    }



      //        return checkFingerprint (fingerprint);

    },
    // vvv---- This is the new bit
    error:   function(jqXHR, textStatus, errorThrown) {
      console.log("Error, status = " + textStatus + ", " +
        "error thrown: " + errorThrown
        );

      //return error
      return callback(errorThrown, null);
    }
  });

}

Javascript: call a blocking HTTP POST

2 Answers2