get client username sent to server side in javascript - node.js

Question

How can I pass form input from client to server in javascript? Below is the client side. I want to take a username or anything entered in textbox, and send it to server.js where it will be processed for validation. the thing is that I need the data from client.js to be stored in a variable in server.js to be able o retreive it.
var textbox;
var dataDiv;
window.onload = init;
function init(){
textbox = document.createElement("input");
textbox.id="textbox";
dataDiv = document.createElement("div");
var header = document.createElement("h1");
header.appendChild(document.createTextNode("Select User"));
var button = document.createElement("BUTTON");
button.id = "myBtn";
var textBtn = document.createTextNode("Click me");
button.appendChild(textBtn);
button.addEventListener("click", () => {
sendData();
});
var docBody = document.getElementsByTagName("body")[0];//Only one body
docBody.appendChild(header);
docBody.appendChild(dataDiv);
docBody.appendChild(textbox);
docBody.appendChild(button);
}
function sendData(){
var usrName = document.getElementById("textbox").value; //I want to send it to server.js
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var dataObj = JSON.stringify(this.responseText);
dataDiv.innerHTML = dataObj;
}
};
xhttp.open("GET", "/register", true);
xhttp.send();
}
This is the server side
var express = require('express');
var app = express();
app.get('/register', handleGetRequest); //how do I pass usrName here?
app.use(express.static('public'));
app.listen(5000);
function handleGetRequest(request, response){
var pathArray = request.url.split("/");
var pathEnd = pathArray[pathArray.length - 1];
if(pathEnd === 'register'){
response.send("{working}");
}
else
response.send("{error: 'Path not recognized'}");
}

Answer 1

If you use GET, you have to put the parameters in the URL.
xhttp.open("GET", "/register?usrName=" + encodeURIComponent(usrName), true);
See How to get a URL parameter in Express? for how you read the query parameter in Express.

Answer 2

Sending data:
function sendData(){
var usrName = document.getElementById("textbox").value; //I want to send it to server.js
var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
if (this.readyState == 4 && this.status == 200) {
var dataObj = JSON.stringify(this.responseText);
dataDiv.innerHTML = dataObj;
}
};
xhttp.open("GET", "http://localhost:5000/register?usrName=" + encodeURIComponent(usrName), true);
xhttp.send();
}
Reading data:
function handleGetRequest(request, response){
var urlParts = request.url.split("?");
if(urlParts[0] === '/register'){
var usrName = urlParts[1].replace('usrName=', '');
response.send("{" + usrName + "}");
}
else
response.send("{error: 'Path not recognized'}");
}