index.html

<html>
<head>
	
</head>
<body>
<script>
/* AjaxHandler interface. */

// var AjaxHandler = new Interface('AjaxHandler', ['request', 'createXhrObject']);

/* SimpleHandler class. */

var SimpleHandler = function() {}; // implements AjaxHandler
SimpleHandler.prototype = {
  request: function(method, url, callback, postVars) {
    var xhr = this.createXhrObject();
    xhr.onreadystatechange = function() {
      if(xhr.readyState !== 4) return;
      (xhr.status === 200) ? 
        callback.success(xhr.responseText, xhr.responseXML) : 
        callback.failure(xhr.status);
    };
    xhr.open(method, url, true);
    if(method !== 'POST') postVars = null;
    xhr.send(postVars);
  },
  createXhrObject: function() { // Factory method.
    var methods = [
      function() { return new XMLHttpRequest(); },
      function() { return new ActiveXObject('Msxml2.XMLHTTP'); },
      function() { return new ActiveXObject('Microsoft.XMLHTTP'); }
    ];
    
    for(var i = 0, len = methods.length; i < len; i++) {
      try {
        methods[i]();
      }
      catch(e) {
        continue;
      }
      // If we reach this point, method[i] worked.
      this.createXhrObject = methods[i]; // Memoize the method.  记住该方法
      return methods[i]();
    }
    
    // If we reach this point, none of the methods worked.
    throw new Error('SimpleHandler: Could not create an XHR object.');
  } 
};

/* Usage. */

var myHandler = new SimpleHandler();
var callback = { 
  success: function(responseText) { alert('Success: ' + responseText); }, 
  failure: function(statusCode) { alert('Failure: ' + statusCode); } 
};
myHandler.request('GET', 'script.php', callback);

</script>​
</body>
</html>