Alert message Response Headers

Question

I’m on a project. NET, in which I create a login page and check the DLL, and in this check, is passed a string of a message that I need to capture with a Typescript to give the alert. This message is already being sent, and it appears there in the page header, as soon as a post is made.

What I need now is to take this message to make a simple alert() and it can appear to the user.

Here is a print that shows how the message is in the header:

I just need to pick her up and do the Alert.

Help me please Thank you.

I’ve tried this code:

var req = new XMLHttpRequest();
    req.open('GET', document.location.href, false);
    req.send(null);
    var headers = req.getAllResponseHeaders().toLowerCase();
    alert(headers);

of this question https://stackoverflow.com/questions/220231/accessing-the-web-pages-http-headers-in-javascript

but I do not see the message, only this data:

I NOTICED SOMETHING ON THE NETWORK

when I post and it returns Alert, the network looks like this:

Note that there is only 1 localhost file

and when I click on the Ubmit button, another localhost file appears that does not contain the header "message":

is created by the code req.send(null);

Observe:

The first localhost contains the message, the last one is generated by req.send(null);

In my TS code la no sources, the following error appears on the line:

req.open("HEAD", window.location.href, false);

Synchronous Xmlhttprequest on the main thread is deprecated because of its detrimental effects to the end user’s Experience. For more help, check in https://xhr.spec.whatwg.org/.

EDIT:

In my file . Cs, where I add the header, has the following code:

public async Task OnPostAsync(PARAMETROS){
      CancellationTokenSource backGroundTask = new CancellationTokenSource();
      MobAtivacaoAcesso MobAtivacaoAcesso = new MobAtivacaoAcesso("X", "Z");

      await MobAtivacaoAcesso.AtivacaoVerificarAsync(PARAMETROS); 

      if (!String.IsNullOrEmpty(MobAtivacaoAcesso.MensagemTemporaria)){
          Response.Headers.Add("mensagem", MobAtivacaoAcesso.MensagemTemporaria);
      }

      return;
}

Answer 1

Why the alert is showing a different header from the answer I can’t tell you, but the way you’re doing it won’t work anyway, because JS doesn’t expect the response of your request to continue running the next line of code, when you do the alert, the server response has not yet arrived.

To run a line of code only after the answer arrives, you need to place these lines within a function, and then pass this function to the property onload of the request. When the answer arrives, this function will be invoked automatically.

var req = new XMLHttpRequest();
    req.open('GET', document.location.href, false);
    req.onload = function() {
        var headers = req.getAllResponseHeaders().toLowerCase();
        alert(headers);
    }
    req.send(null);

Answer 2

First, "message" is not a "valid" header, I really don’t know why this wanting to do this way, headers are usually browser instructions, content BODY should be the place to use something like this, like a reply JSON, I don’t see why you want to reinvent the wheel.

Now let’s get to the problem, in a simple test, with a code like this:

var request = new XMLHttpRequest;

request.open('GET', 'teste.php', false);

request.send(null);
console.log(request.getAllResponseHeaders());

I was returned to console.log:

date: Thu, 23 May 2019 15:33:52 GMT
guilherme: brcontainer
server: Apache/2.4.3 (Win64)
content-type: text/html; charset=UTF-8
mensagem: teste
connection: Keep-Alive
keep-alive: timeout=5, max=99
content-length: 1

That is was returned the headers correctly, with alert also returned perfectly:

A probable explanation:

This using different domains

If you are using different domains, ie Ajax is on one page and the link requested in another, would have to set the Access-Control-Expose-Headers with mensagem to expose the custom header.

Using some add-on/extension

Using some add-on/extension that somehow overrides the HTTP transport, only returning what is of interest (this is just my speculation)

Your browser is outdated

As amazing as it sounds, the test I took was on Chrome 74.0.3729.169 and worked perfectly

---

To try to solve

If you’ve already updated Chrome to the latest version then create a page without jQuery (I can’t say if jQuery overwrites something, but nowadays I don’t doubt anything like that), an empty HTML with only its basic code and open in an anonymous tab (ensure that no add-on runs in private), so:

<html>
<body>
<script>
var request = new XMLHttpRequest;

request.open('GET', window.location.href, false);

request.send(null);
alert(request.getAllResponseHeaders());
</script>
</body>
</html>

---

How to get an answer without using headers

As I said at the beginning of the answer, why reinvent the wheel, unlisted headers usually use the prefix x-, which indicates experimental or "non-standard", is your case, that header your mensagem was invented by you, of course it works in the tests done, but not really why transform a bike on a "bike", first, outside the Web Workers do not use XMLHttpRequet synchronous, asynchronous use, has nothing to do with the solution, but rather because outside of Web Workers this is obsolete, still works, but is considered as such. So instead of picking up all headers try to pick up only the one of interest with request.getResponseHeader("mensagem")

Example:

function resposta(url, callback)
{
    var request = new XMLHttpRequest;

    request.open('GET', url, true);//Terceiro parametro TRUE

    request.onreadystatechange = function () {
        //Se ainda não estiver concluido (diferente de 4) ele interrompe o script, irá tentar sozinho novamente em seguida
        if (request.readyState !== 4) return;

        callback(request.getResponseHeader("mensagem"));
    };

    request.send(null);
}

And to wear something like that:

resposta(window.location.href, function (resposta) {
    alert(resposta);
});

Now really if it is a data that comes from the bank really do not see why to do this, it is better to create a URL/ route just for that, with a response in TXT or JSON, something like:

    var request = new XMLHttpRequest;

    request.open('GET', 'status.aspx', true);//Pode ser uma rota se for asp.net-mvc

    request.onreadystatechange = function () {
          //Se ainda não estiver concluido (diferente de 4) ele interrompe o script, irá tentar sozinho novamente em seguida
          if (request.readyState !== 4) return;

          callback(request.responseText); //responseText retorna o BODY da resposta HTTP
    };

    request.send(null);

In your status.aspx put the result of what would be the message directly in the body, something like:

<% Response.Write("sua mensagem aqui"); %>

Route error (on server side)

Probably your error is in the routes, the page that this, the page before of the call XMLHttpRequest is in POST and when calls with XMLHttpRequest is using GET, so probably some configuration your this made the header only sent when POST.