如何从服务器获取响应？ （PHP，JS，HTML）

<!--index.html-->
<script>
  function work()
  {
    var ajax = new XMLHttpRequest();
    ajax.open("POST", "doWork.php");
    ajax.send("doIt");           
  }
</script>
<button onClick="work();" />

,

<!--doWork.php-->
<?php
  echo "Loading...";
  hardWork1(); // or maybe sleep(10);
  echo "Completed number xxx";
?>

Hi, I want to get two messages or more in sequence from the server.

Like above code, such as "Loading..." before "Completed Number xxx".

Do I have to add another AJAX send in first AJAX's callback?

Do you want something like this?

<div id="content">
Loading...
</div>

…
if(ajax.readyState == 4 && ajax.status == 200){
    document.getElementById().innerHTML = 'Completed Number ' + ajax.responseText;
}
…