JSFiddle - React, Tailwind, and code Playground

HTML

<form id="requestForm">
    <input type="text" name="fName" id="name">
    <input type="text" name="fAddress" id="address">
    <input type="text" name="fComment" id="comment">

    <input type="submit" value="Submit" name="nameSubmit">
</form>

JavaScript

document.querySelector('#requestForm').addEventListener('submit', postRequest);

        function postRequest(e){
            e.preventDefault();

            const params = {

                fName: document.querySelector('#name').value,
                fAddress: document.querySelector('#address').value,
                fComment: document.querySelector('#comment').value,

            };
            var xhr = new XMLHttpRequest();
            xhr.open('POST', '/echo/html/');
            xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
            xhr.onload = function(){ }
            
            xhr.send(getReadyToSend(params));
        } 
        
        function getReadyToSend(object) {
    var objList = [];
    for (var prop in object) {
        if (object.hasOwnProperty(prop)) {
            objList.push(encodeURI(prop + '=' + object[prop]));
        }
    }
    return objList.join("&");
}