How to send a post request to a servlet via javascript?

I am writing a web service interested in the following script.

1. There is an html file with a table and a button.
2. When you select a field in the table, the field is assigned a new class "active"
3. I click on the button
4. I wish in the servlet to get the data that is in the first column of the selected field.

The question is how to organize a post-request to the servlet via js and send the data?

Now, if we take data from the form, then everything works out correctly.

And I would like not to resort to using the form, but let the script run around the required data and send it all over the entire Html file.

Script file:

function getXmlHttp() { var xmlHttp = null; if (window.XMLHttpRequest) { xmlHttp = new XMLHttpRequest(); } else if (window.ActiveXObject) { xmlHttp = new ActiveXObject("Microsoft.XMLHTTP"); } return xmlHttp; } function httpReq(URL, method, data, success, error) { var request = getXmlHttp(); request.open(method, URL, true); request.setRequestHeader("Content-type", "multipart/form-data"); request.send(data); request.onreadystatechange = function() { if (request.readyState == 4) { if (request.status == 200) { success(request.responseText); } else { if (error) error(request.status); } } } } var table = document.querySelector("#selectTable") var field = table.querySelector(".active"); var item = field.children[0]; // первый дочерний var form = new FormData(); form.append("some_key", item.innerHTML); // ну или что там нужно вытащить httpReq("/admin", "POST", form, function(res) { console.log("response:", res); });