好的，这个问题被问了很多，回答了很多，大多数提问者都有概念问题。我将分部分对此进行解释，之后我将对您的代码进行干净的重写，包括一个javascript文件，供您深入学习

• 您试图做的事情背后的想法涉及到最有可能是静态html页面的部分的某种行为
• Javascript将行为添加到原本已经失效的html中，允许您触发事件并生成响应
• Ajax诞生于一种集体需求，即在用户不离开页面的情况下能够与服务器对话。它允许我们在后台发出请求（异步）并带回信息
• 将行为与异步请求相结合的能力是当今丰富的互联网应用程序（简称RIA？）的基础

好吧，不要从表面上看，做一些研究，你会发现它的潜力。同时，我会创建一个你想要的模型，我会尽快回来。注意其他答案，周围有很多知识渊博的人

编辑

html表单

<form method="somemethod" action="somescript.php">
  <select name="lst_tour" id="lst_tour">
    <option value="">Select a Tour:</option>
    <?php foreach ( $results as $option ) {
      ?><option value="<?php echo $option->departure_date; ?>"><?php echo $option->departure_date; ?></option><?php
    } ?></select>
  <!-- these will be "magically" populated, they conveniently have ids ^^ -->
  <input name="txt_tourname" type="text" id="txt_tourname" readonly="readonly" />
  <input name="txt_departuredate" type="text" id="txt_departuredate" readonly="readonly" />
  <input name="txt_tourdetails" type="text" id="txt_tourdetails" readonly="readonly" />
</form>

javascript

大量的编辑和重写。这是一个有很多alerts的嘈杂脚本，所以请耐心等待，并在您不再需要警报时按顺序开始删除警报注意：select标记有一个id，我用它来查找它并附加事件处理程序

(function(){
  var
    // the php script that's taking care of business
    url = 'http://path/to/handling/ajaxscript.php',
    select,
    // assume these are the ids of the fields to populate
    //  AND assume they are the keys of the array thats comming from the server
    inputs = ['txt_tourname','txt_departuredate','txt_tourdetails'],
    // the XMLHttpRequest, I'm not recycling it but, oh well
    xhr,
    // the onReadyStateChange handler function, it needs access to xhr
    xhrRSC,
    // event handler, called for <select>."onChange"
    onChooseDate,
    // response handler that will be executed once the xhrRSC deems it ready
    populateData,
    // convenient event handlers
    onLoad, onUnload;
  xhrRSC = function () {
    if (xhr && xhr.readyState !== 4) {return;}
    alert('the server response has completed. Now continue with the population');
    populateData(JSON.parse(xhr.responseText));
    xhr = null;
  };
  onChooseDate = function () {
    var date = select.options[select.selectedIndex].value;
    alert('I have been changed. Did I select the right date: '+date
      +'. Now we send some info to the server');
    // AJAX: make xhr
    xhr = new XMLHttpRequest();
    // AJAX: setup handler
    xhr.onreadystatechange = xhrRSC;
    // AJAX: open channel
    xhr.open('get',url+'?ajax=1&date='+date,true);
    // AJAX: send data (if method post)
    xhr.send(null);
    // if we had jQuery, we could condense all this into one line
    // $.post(url,{ajax:1,date:date},populateData,'json');
  };
  populateData = function (json) {
    // we have the content from the server. Now json decode it
    alert('json data => '+json.toSource());
    // foreach input id execute function
    inputs.forEach(function(v){
      // set the value of each input to the data sent by the server
      alert('setting input "'+v+'" to "'+json[v]+'"');
      document.getElementById(v).value = json[v];
    });
  };
  onLoad = function () {
    alert('page has loaded');
    // assume the <select> tag has an id of "lst_tour", just as it's name
    select = document.getElementById('lst_tour');
    // the "change" event is fired when the user changes the selected <option>
    select.addEventListener('change',onChooseDate,false);
  };
  onUnload = function () {
    select.removeEventListener('change',onChooseDate,false);
    select = null;
  };
  window.addEventListener('load',onLoad,false);
  window.addEventListener('unload',onUnload,false);
}());

ajax脚本，php处理程序

<?php
// this file has $_GET populated with 'ajax' => '1' and 'date' => 'what the user chose'
if (!isset($_GET['ajax'])) die('this is not how its supposed to work');
// we must protect the output
ob_start();
// your initializers
// your logic: it should make the selection, then populate the array to be JSON encoded
$response = array(
  'txt_tourname' => $txt_tourname,
  'txt_departuredate' => $txt_departuredate,
  'txt_tourdetails' => $txt_tourdetails
);
// you may want to log this for debugging
// server output has been protected
ob_end_clean();
header('Content-Type: text/json');
echo json_encode($response);
// the client has what he wanted
exit;

它是这样的，它没有经过测试，而且是一个手工的，但经过仔细的审查，你会学到很多。另请阅读Crockford，并考虑到使用jQuery的好处，即使用jQuery