How do I get JSON response from a route?

let xhr = new XMLHttpRequest();
let method = "GET";
const url = "http://127.0.0.1:5000/cars";

xhr.open(method, url, true);
xhr.setRequestHeader("Content-Type", "application/json");
xhr.onreadystatechange = function() {
  if (xhr.readyState === XMLHttpRequest.DONE) {
    if (xhr.status === 200) {
      const data = JSON.parse(xhr.responseText);
      console.log(data);

      // getElementsByClassName returns an array of elements.
      // querySelector returns a single element based on a CSS selector.
      document.querySelector(".car_name").innerHTML = data.info[1]
      document.querySelector(".car_price").innerHTML = data.info[2]
    } else {
      // statusText shows the status message of the request.
      alert(xhr.statusText);
      window.location.reload();
    }
  }
};
xhr.send(null);

let method = "GET";
const url = "http://127.0.0.1:5000/cars";

fetch(url, {
  method,
  headers: {
    "Content-Type": "application/json"
  }
}).then(response => {
  if (!response.ok) {
    throw new Error(`Fetching JSON went wrong - ${response.statusText}`);
  }

  return response.json();
}).then(data => {
  console.log(data);

  document.querySelector(".car_name").innerHTML = data.info[1]
  document.querySelector(".car_price").innerHTML = data.info[2]
}).catch(error => {
  alert(error);
  window.location.reload();
});