How to make an AJAX call without jQuery

app.js

// Using vanilla JS (no jQuery)

// Your API key
var apiKey = "your-key-goes-here"
  // Typically the URL will contain a key and other parameters (depending on the API you're making a call to)
var apiUrl = "the-API-URL-goes-here" + apiKey;

// Create the XMLHttpRequest object (allows us to make an AJAX call to an API)
// See more here: https://developer.mozilla.org/en/docs/Web/API/XMLHttpRequest

var xhr = new XMLHttpRequest();

// When the request is ready
xhr.onreadystatechange = function() {

  // if the request is done
  if (xhr.readyState == XMLHttpRequest.DONE) {

    // and the status is 200 (which means we made it ok to the other end)
    if (xhr.status == 200) {

      // The response from the API is recieved via responseText
      // parse the response so we can traverse it
      var data = JSON.parse(xhr.responseText);

      // Do something with this "data", append to the DOM, output to console..

    // If the requests fails or something's wrong..       
    } else {
      // Output the response text (proabably contains an error messsage to the console);       
      console.log(repsonseText);
    }
  }
};

// Make the call
xhr.open("GET", apiUrl, true);

// Send the crendtials and acutal request
xhr.send();