Sending Http POST Request through Rest API in Javascript

I am trying to send an Http post request to parse.com server through Rest API keys. Not sure if I am doing it right as below. The following is my whole script and makes a button which should trigger the post request in a simple HTML page.

<input id="clickMe" type="button" value="clickme" onclick="doFunction();" />
<script>

xmlhttp = new XMLHttpRequest();
var url = "https://api.parse.com/1/classes/english";
xmlhttp.open("POST", url, true);
xmlhttp.setRequestHeader("Content-type", "application/json");
xmlhttp.setRequestHeader("X-Parse-Application-Id", "VnxVYV8ndyp6hE7FlPxBdXdhxTCmxX1111111");
xmlhttp.setRequestHeader("X-Parse-REST-API-Key","6QzJ0FRSPIhXbEziFFPs7JvH1l11111111");
xmlhttp.onreadystatechange = function () { //Call a function when the state changes.
    if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
        alert(xmlhttp.responseText);
    }
}
var parameters = {
    "ephrase": "english",
    "pphrase": "farsi",
     "nvote": 0,
    "yvote": 0
};
// Neither was accepted when I set with parameters="username=myname"+"&password=mypass" as the server may not accept that

function doFunction() {
  xmlhttp.send(parameters);
}

</script>