Make HTTP POST using XMLHttpRequest

xhrpost.js

var xhr = new XMLHttpRequest();
url = '/url/to/post';
params = JSON.stringify({'key': 'value'});
xhr.open("POST", url, true);

xhr.setRequestHeader("Content-Type", "application/json");
xhr.setRequestHeader("Content-Length", params.length);
xhr.setRequestHeader("Connection", "close");

xhr.onreadystatechange = function() {
    if (this.status == 200) {
        console.log(this.responseText);
    }
}
xhr.send(params);