The 30 second AJAX Tutorial

Taken from the php-general mailing list. [ Mail by Rasmus on AJAX ]

I find a lot of this AJAX stuff a bit of a hype.  Lots of people have

been using similar things long before it became "AJAX".  And it really

isn't as complicated as a lot of people make it out to be.  Here is a

simple example from one of my apps.

First the Javascript:function createRequestObject()

 {

    var ro;

    var browser = navigator.appName;

    if(browser == "Microsoft Internet Explorer"){

        ro = new ActiveXObject("Microsoft.XMLHTTP");

    }

    else{

       ro = new XMLHttpRequest();
        }

    return ro;

}

var http = createRequestObject();

function sndReq(action) {

    http.open('get', 'rpc.php?action='+action);

    http.onreadystatechange = handleResponse;

    http.send(null);

}

function handleResponse() {

    if(http.readyState == 4){

        var response = http.responseText;

        var update = new Array();

if(response.indexOf('|' != -1)) {

            update = response.split('|');

            document.getElementById(update[0]).innerHTML = update[1];

        }

    }

}

This creates a request object along with a send request and handle

response function.  So to actually use it, you could include this js in

your page.  Then to make one of these backend requests you would tie it

to something.  Like an onclick event or a straight href like this:

<a href="javascript:sndReq('foo')">[foo]</a>

That means that when someone clicks on that link what actually happens

is that a backend request to rpc.php?action=foo will be sent.

In rpc.php you might have something like this:

switch($_REQUEST['action']) {

    case 'foo':

      / do something /

      echo "foo|foo done";

      break;

    ...

  }

Now, look at handleResponse.  It parses the "foo|foo done" string and

splits it on the '|' and uses whatever is before the '|' as the dom

element id in your page and the part after as the new innerHTML of that

element.  That means if you have a div tag like this in your page:

<div id="foo">

  </div>

Once you click on that link, that will dynamically be changed to:

<div id="foo">

  foo done

  </div>

That's all there is to it.  Everything else is just building on top of

this.  Replacing my simple response "id|text" syntax with a richer XML

format and makine the request much more complicated as well.  Before you

blindly install large "AJAX" libraries, have a go at rolling your own

functionality so you know exactly how it works and you only make it as

complicated as you need.  Often you don't need much more than what I

have shown here.

Expanding this approach a bit to send multiple parameters in the

request, for example, would be really simple.  Something like:

function sndReqArg(action,arg) {

    http.open('get', 'rpc.php?action='+action+'&arg='+arg);

    http.onreadystatechange = handleResponse;

    http.send(null);

  }

And your handleResponse can easily be expanded to do much more

interesting things than just replacing the contents of a div.

-Rasmus