[sash003]

Полный вариант, не супер но сойдёт

function ajax(obj){
      
    try{var xhr = new XMLHttpRequest()
    } catch(e1){try{
       var xhr = new ActiveXObject("Msxml2.XMLHTTP")
      } catch(e2){try{
          var xhr = new ActiveXObject("Microsoft.XMLHTTP")
        } catch(e3){var xhr = false
        }
      }
    }
      obj.type = obj.type || "GET" ;
      if(obj.type === 'POST'){
          xhr.open("POST", obj.url, true);
          var params = '';
          if (typeof obj.data === 'string')
          params = obj.data;
          else if(typeof obj.data === 'object'){
              
              if(obj.contentType === false){
                 params = obj.data;
                 console.log(params); 
              }
          else{   
          for(var i in obj.data){
          params += i + '=' + obj.data[i] + '&';
          }
          params = params.slice(0, -1);
          console.log(params)
          xhr.setRequestHeader("Content-type",
          "application/x-www-form-urlencoded");   
          }
          xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");     }
          xhr.onreadystatechange = function() { 
          if(xhr.readyState == 4 && xhr.status == 200){
          obj.success(this['response' + obj.dataType]);
          }
          else console.log( "Ajax error: " + this.statusText);
          }
          xhr.send(params);
      }
      else if(obj.type === "GET"){
          var params = '?';
          if (typeof obj.data === 'string')
          params += obj.data;
          else if(typeof obj.data === 'object'){
           for(var i in obj.data){
              params += i + '=' + encodeURIComponent(obj.data[i]) + '&'
          }
          params = params.slice(0, -1);
          params += "&nocache=" + Math.random() * 1000000;   
          }
          xhr.open("GET", obj.url + params, true);
          xhr.setRequestHeader("X-Requested-With", "XMLHttpRequest");
          xhr.onreadystatechange = function() { 
          if(this.readyState == 4 && this.status == 200){
          obj.success(this['response' + obj.dataType]);    
          }
          else console.log( "Ajax error: " + this.statusText)
          }
          xhr.send(null);
      }
  }

document.forms.f1.onsubmit = function(e){
      e.preventDefault();
      var formObj = {};
      var elem = document.forms.f1;
      var inputs = elem.querySelectorAll('[name]');
      for(var i = 0; i < inputs.length; i++){
      formObj[inputs[i].name] = inputs[i].value;
      if(window.FormData) {
      var formData = new FormData(document.forms.f1);     
      } 
      }
      // попытка отправки 
      ajax({
      url : './test_ajax.php',
      type: 'POST',
      dataType: 'Text',
      contentType : false,
      data:formData,//{text: document.querySelector('[name=text]').value, _data_ : 'true'},
      success: function(response){
          document.getElementById('response').innerHTML =
                response;
      }
  });
    }