​x
 
<!DOCTYPE html>
<html>
<script>
function myfunction() {
  const xhttp = new XMLHttpRequest();
  xhttp.open("POST", "/demo/php/ajax.php");
  xhttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xhttp.onload = function() {
    document.getElementById("demo").innerHTML = this.responseText;
  }
  xhttp.send("fname=Mary");
}
</script>
<body>
​
<button onclick="myfunction()">点击我！</button>
​
<h1 id="demo"></h1>
​
</body>
</html>