how to send data with xmlhttprequest code example

Example 1: xmlhttp js post request

var xhr = new XMLHttpRequest();
xhr.open("POST", '/url', true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");

xhr.onreadystatechange = function() { // Call a function when the state changes.
    if (this.readyState === XMLHttpRequest.DONE && this.status === 200) {
        // Request finished. Do processing here.
    }
}
xhr.send("name=Hello&id=world");

Example 2: xhr post send

var xhr = new XMLHttpRequest();
var params = 'field1='+postfield1+'&field2='+postfield2;
xhr.open('POST', 'http://exmaple.com', true);

//Send the proper header information along with the request
xhr.setRequestHeader('Content-type', 'application/x-www-form-urlencoded');

xhr.onload = function() {//Call a function when the state changes.
    if(xhr.status == 200) {
        alert(this.responseText);
    }
}
xhr.send(params);

Example 3: javascript send post data with ajax

function makeRequest (method, url, data) {
  return new Promise(function (resolve, reject) {
    var xhr = new XMLHttpRequest();
    xhr.open(method, url);
    xhr.onload = function () {
      if (this.status >= 200 && this.status < 300) {
        resolve(xhr.response);
      } else {
        reject({
          status: this.status,
          statusText: xhr.statusText
        });
      }
    };
    xhr.onerror = function () {
      reject({
        status: this.status,
        statusText: xhr.statusText
      });
    };
    if(method=="POST" && data){
        xhr.send(data);
    }else{
        xhr.send();
    }
  });
}

//POST example
var data={"person":"john","balance":1.23};
makeRequest('POST', "https://www.codegrepper.com/endpoint.php?param1=yoyoma",data).then(function(data){
              var results=JSON.parse(data);
});