XMLHttpRequest를 사용하여 JavaScript로 POST 데이터를 보내려면 어떻게 해야 합니까?

<form name="inputform" action="somewhere" method="post">
  <input type="hidden" value="person" name="user">
  <input type="hidden" value="password" name="pwd">
  <input type="hidden" value="place" name="organization">
  <input type="hidden" value="key" name="requiredkey">
</form>

var http = new XMLHttpRequest();
var url = 'get_data.php';
var params = 'orem=ipsum&name=binny';
http.open('POST', url, true);
http.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');

http.onreadystatechange = function() {
    if(http.readyState == 4 && http.status == 200) {
        alert(http.responseText);
    }
}
http.send(params);

var params = new Object();
params.myparam1 = myval1;
params.myparam2 = myval2;

let urlEncodedData = "", urlEncodedDataPairs = [], name;
for( name in params ) {
    urlEncodedDataPairs.push(encodeURIComponent(name)+'='+encodeURIComponent(params[name]));
}