如何将ajax请求从jQuery纯js转换？

var xhr = new XMLHttpRequest();
xhr.open('GET', 'http://example.com/api', true);
xhr.setRequestHeader('Content-Type', 'application/json');
xhr.onreadystatechange = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    var response = JSON.parse(xhr.responseText);
    console.log(response);
  }
};
xhr.send();