javascript的一些总结(8)

[b]16.通用的ajax库[/b]

var ajaxreq=false, ajaxCallback;
// ajaxRequest: Sets up a request
function ajaxRequest(filename) {
   try {
    // Firefox / IE7 / Others
    ajaxreq= new XMLHttpRequest();
   } catch (error) {
    try {
      // IE 5 / IE 6
      ajaxreq = new ActiveXObject("Microsoft.XMLHTTP");
    } catch (error) {
      return false;
    }
   }
   ajaxreq.open("GET",filename);
   ajaxreq.onreadystatechange = ajaxResponse;
   ajaxreq.send(null);
}
// ajaxResponse: Waits for response and calls a function
function ajaxResponse() {
   if (ajaxreq.readyState !=4) return;
   if (ajaxreq.status==200) {
      // if the request succeeded...
      if (ajaxCallback) ajaxCallback();
   } else alert("Request failed: " + ajaxreq.statusText);
   return true;
}

ajax的小例子

<html>
<head><title>Ajax Test</title>
<script language="JavaScript" type="text/javascript"
   src="ajax.js">
</script>
</head>
<body>
<h1>Ajax Quiz Example</h1>
<form>
<p><b>Question:</b>
<span id="question">...
</span>
</p>
<p><b>Answer:</b>
<input type="text" name="answer" id="answer">
<input type="button" value="Submit" id="submit">
</p>
<input type="button" value="Start the Quiz" id="startq">
</form>
<script language="JavaScript" type="text/javascript"
   src="quiz.js">
</script>
</body>
</html>

<?xml version="1.0" ?>
<questions>
    <q>What DOM object contains URL information for the window?</q>
    <a>location</a>
    <q>Which method of the document object finds the object for an element?</q>
    <a>getElementById</a>
    <q>If you declare a variable outside a function, is it global or local?</q>
    <a>global</a>
    <q>What is the formal standard for the JavaScript language called?</q>
    <a>ECMAScript</a>
</questions>

var qn=0;
// load the questions from the XML file
function getQuestions() {
   obj=document.getElementById("question");
   obj.firstChild.nodeValue="(please wait)";
   ajaxCallback = nextQuestion;
   ajaxRequest("questions.xml");
}
// display the next question
function nextQuestion() {
   questions = ajaxreq.responseXML.getElementsByTagName("q");
   obj=document.getElementById("question");
   if (qn < questions.length) {
      q = questions[qn].firstChild.nodeValue;
      obj.firstChild.nodeValue=q;
   } else {
      obj.firstChild.nodeValue="(no more questions)";
   }
}
// check the user's answer
function checkAnswer() {
   answers = ajaxreq.responseXML.getElementsByTagName("a");
   a = answers[qn].firstChild.nodeValue;
   answerfield = document.getElementById("answer");
   if (a == answerfield.value) {
      alert("Correct!");
   }
   else {
      alert("Incorrect. The correct answer is: " + a);
   }
   qn = qn + 1;
   answerfield.value="";
   nextQuestion();
}
// Set up the event handlers for the buttons
obj=document.getElementById("startq");
obj.onclick=getQuestions;
ans=document.getElementById("submit");
ans.onclick=checkAnswer;