an example of send an ajax request

ajax_get.js

nocache = "&nocache=" + Math.random() * 1000000
request = new ajaxRequest()
request.open("GET", "urlget.php?url=oreilly.com" + nocache, true)
// 与post相比， get 请求不需要设置header

request.onreadystatechange = function()
{
    if (this.readyState == 4)
    {
          if (this.status == 200)
          {
               if (this.responseText != null)
               {
                     document.getElementById('info').innerHTML = this.responseText
               }
               else alert("Ajax error: No data received")
          }
          else alert( "Ajax error: " + this.statusText)
    }
}

request.send(null)

function ajaxRequest()
{
    try
    {
          var request = new XMLHttpRequest()
    }
    catch(e1)
    {
          try
          {
               request = new ActiveXObject("Msxml2.XMLHTTP")
          }
          catch(e2)
          {
               try
               {
                     request = new ActiveXObject("Microsoft.XMLHTTP")
               }
               catch(e3)
               {
                     request = false
               }
          }
    }
    return request
}

ajax_post.js

params = "url=oreilly.com"
request = new ajaxRequest()

// Specifies the HTTP method to use (GET or POST), the target URL, and
// whether the request should be handled asynchronously (true or false)
request.open("POST", "urlpost.php", true)
// Sets a header with a parameter/value pair
request.setRequestHeader("Content-type", "application/x-www-form-urlencoded")
request.setRequestHeader("Content-length", params.length)
request.setRequestHeader("Connection", "close")

//Specifies an event handling function to be called whenever the readyState property of an object changes.
request.onreadystatechange = ajaxCallBack

// Sends data to the target server using the specified HTTP method
request.send(params)


function ajaxCallBack()
{
    // An integer property that reports on the status of a request. 
    // It can have any of these values: 
    // 0 = Uninitialized, 1 = Loading, 2 = Loaded, 3 = Interactive, and 4 = Completed.
    if (this.readyState == 4)
    {
          // The HTTP status code returned by the server.
          if (this.status == 200)
          {    // The data returned by the server in text format.
               if (this.responseText != null)
               {
                     document.getElementById('info').innerHTML =
                          this.responseText
               }
               else alert("Ajax error: No data received")
          }
          // The HTTP status text returned by the server.
          else alert( "Ajax error: " + this.statusText)
    }
}


function ajaxRequest()
{
    try // Non-IE browser?
    {
        var request = new XMLHttpRequest()
    }
    catch(e1)
    {
          try // IE 6+?
          {
            request = new ActiveXObject("Msxml2.XMLHTTP")
          }
          catch(e2)
          {
               try // IE 5?
               {
                request = new ActiveXObject("Microsoft.XMLHTTP")
               }
               catch(e3) // There is no Ajax support
               {
                     request = false
               }
          }
    }
    return request
}