AJAX javascript, PHP post does not work

Question

Good morning, I’m created a code Java to send data using AJAX to a PHP page,my problem is that the POST is going empty to page I’m calling. This only happens when I call the Javascript (AJAX) function that makes the request, when I call the PHP page straight through the action POST works normally. What can it be?

 function AjaxExecute(arquivo){
        var ajax;

        if(window.XMLHttpRequest){ 

            ajax = new XMLHttpRequest();

        } else {

            try{
                ajax = new ActiveXObject("Msxml2.XMLHTTP");
            }catch(e){
                ajax = new ActiveXObject("Microsoft.XMLHTTP");
            }   
        }

        ajax.onreadystatechange = function(){

            if(ajax.readyState == 4 && ajax.status == 200){

                return this.responseText;
            }
        }

        ajax.open("post",arquivo);
        ajax.send(null);

}

Answer 1

Is missing the url, and define the header:

...
var url = "receberFicheiro.php";
ajax.open("post", url, "true");
ajax.setRequestHeader("Content-type", "multipart/form-data");
ajax.onreadystatechange = function(){
   if(ajax.readyState == 4 && ajax.status == 200){
      # ???
      return this.responseText;
   }
}
ajax.send(ficheiro);

And attention to return.

Answer 2

1. Trade the Return for a callback (read this What is the real advantage of using a Callback and what is thread/multithread?)

2. And finally adjust if to detect HTTP or connection errors:

3. Then adjust the header to use POST (read this AJAX Javascript Pure Asynchronous)

   function AjaxExecute(arquivo, variaveis, success, fail){
       var ajax;
   
       variaveis = !variaveis ? null : variaveis;
   
       if(window.XMLHttpRequest){ 
   
           ajax = new XMLHttpRequest();
   
       } else if (window.ActiveXObject) {
   
           try{
               ajax = new ActiveXObject("Msxml2.XMLHTTP");
           }catch(e){
               ajax = new ActiveXObject("Microsoft.XMLHTTP");
           }
       } else {
           //Simula um erro acaso Ajax não esteja disponivel (quase improvavel)
           setTimeout(error, 1, 0);
           return;
       }
   
       ajax.onreadystatechange = function(){
   
           if(ajax.readyState == 4){
               if (ajax.status == 200) {
                   //Callback se retornar status HTTP 200
                   success(this.responseText);
               } else {
                   //Calllback se retornar qualquer outro status até 0 (sem conexão)
                   fail(ajax.status);
               }
           }
       }
   
       ajax.open("post", arquivo);
   
       //Ajusta a requisição para trabalhar o POST
       ajax.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
   
       //Envia os dados via POST
       ajax.send(variaveis);
   }
   
   function sucesso(resposta) {
       alert(resposta);
   }
   
   function erro(codigo) {
       alert("Erro na requisição:" + codigo);
   }
   
   AjaxExecute("pagina.php", "foo=1&bar=2", sucesso, erro);