how can I update value of input text via ajax?

I want to have

• an input text box that I can
• update its value with AJAX call ('get current revision') and then
• another button ( "update code base" ) to make another AJAX call the value in the text box

I do not know how to combine all this together.

<form action="upgag开发者_C百科e.php">
  revision <input type="text" name="revision" value="" /><br />
  <input type="submit" value="update code base" />
<input type="submit" value="get current revision" />

</form>

I would like to use only javascript not jQuery

<form action="upgage.php">
  <input type="submit" id="revision"/> <input type="text" id="passedValue" value="" /><br />
  <input type="submit" value="update" />
</form>

now in jQuery:

$("#revision").click(function(event) {
  event.preventDefault();
   $.post("/my/url/", function(data) {
      $("#passedValue").val(data);
   });

});

Hope I understood you correctly :P

<script>
    document.getElementById('getValueButton').onclick = function() {
        document.getElementById('revisionTextField').value = getRevisionViaAjax();
    }
</script>