js json send

js_post_json.js

var xhr = new XMLHttpRequest();

xhr.onreadystatechange = function () {
    if (this.readyState != 4) return;

    if (this.status == 200) {
        var data = JSON.parse(this.responseText);

        // we get the returned data
    }

    // end of state change: it can be after some time (async)
};

xhr.open("POST", yourUrl, true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.send(JSON.stringify({
    value: value
}));