Question

I have such part of code:

var xhr = new XMLHttpRequest();
xhr.open("POST", "http://someurl.com", true);
xhr.setRequestHeader("Content-Type","application/x-www-form-urlencoded");
xhr.onreadystatechange = function() {
  if (xhr.readyState == 4) {
    if (xhr.status == 200) {
      doSomeTask();
    }
  }
}
xhr.send('login=mylogin&password=mypassword');

How can I know if my login&password are correct? In both cases xhr.status is 200.

Answer 1

Invalid Login/Password attempts are not HTTP failures. Only HTTP Failures return you 4xx or 5xx return codes. You might want to use the xhr.responseText or xhr.responseXML from the response to see what your backend is returning and base your decision according to that. Please refer to http://www.w3.org/TR/2006/WD-XMLHttpRequest-20060405/#dfn-responsetext for how the responses are obtained.

Also, there are tons of good Javascript framework that hide the complexity of making Ajax calls. JQuery makes the job of calling AJAX scripts extremely easy. You might want to investigate on that instead of writing raw XHR code.