Slide 13.4: AJAX sending a request to a server

AJAX Sending a Request to a Server

Let AJAX change this text.

Sending an XMLHttpRequest to a Server
The XMLHttpRequest object is used to exchange data with a server. To send a request to a server, we use the open and send methods of the XMLHttpRequest object:

   xmlhttp.open( "GET", "AJAX_info.txt", true );
   xmlhttp.send( );

Method	Description
`open(method,url,async )`	Specifies the type of request, the URL, and if the request should be handled asynchronously or not. `method`: the type of request: GET or POST `url`: the location of the file on the server `async`: true (asynchronous) or false (synchronous)
`send(string)`	Sends the request off to the server. `string`: Only used for POST requests

GET or POST?
GET is simpler and faster than POST, and can be used in most cases. However, always use POST requests when:

A cached file is not an option (update a file or database on the server).

Sending a large amount of data to the server (POST has no size limitations).

Sending user input (which can contain unknown characters), POST is more robust and secure than GET.

<script type="text/javascript">
  function loadXMLDoc( ) {
    var xmlhttp;
    if ( window.XMLHttpRequest ) {
      // code for IE7+, Firefox, Chrome, Opera, Safari
      xmlhttp = new XMLHttpRequest( );
    }
    else {
      // code for IE6, IE5
      xmlhttp = new ActiveXObject( "Microsoft.XMLHTTP" );
    }
    xmlhttp.onreadystatechange = function( ) {
      if ( ( xmlhttp.readyState == 4 ) && 
           ( xmlhttp.status     == 200 ) ) {
        document.getElementById("myDiv").innerHTML =
          xmlhttp.responseText;
      }
    }
    xmlhttp.open( "GET", "AJAX_info.txt", true );
    xmlhttp.send( );
  }
</script>