Simple Ajax Example

Ajax is the method of using Javascript, DHTML and the XMLHttpRequest object to perform a GET or POST and return a result without reloading the HTML page. Below is a very simple Ajax example that calls a CGI script that prints out the word sent to the CGI script and the remote user's IP address.

Simple Ajax Demo

word:

HTML page

This is the HTML page with three JavaScript functions that perform the XMLHttpRequest and subsequent update to the HTML page. (These are Ajax calls)

<html>
<head>
<title>Simple Ajax Example</title>
<script language="Javascript">
function xmlhttpPost(strURL) {
    var xmlHttpReq = false;
    var self = this;
    // Mozilla/Safari
    if (window.XMLHttpRequest) {
        self.xmlHttpReq = new XMLHttpRequest();
    }
    // IE
    else if (window.ActiveXObject) {
        self.xmlHttpReq = new ActiveXObject("Microsoft.XMLHTTP");
    }
    self.xmlHttpReq.open('POST', strURL, true);
    self.xmlHttpReq.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    self.xmlHttpReq.onreadystatechange = function() {
        if (self.xmlHttpReq.readyState == 4) {
            updatepage(self.xmlHttpReq.responseText);
        }
    }
    self.xmlHttpReq.send(getquerystring());
}

function getquerystring() {
    var form     = document.forms['f1'];
    var word = form.word.value;
    qstr = 'w=' + escape(word);  // NOTE: no '?' before querystring
    return qstr;
}

function updatepage(str){
    document.getElementById("result").innerHTML = str;
}
</script>
</head>
<body>
<form name="f1">
  <p>word: <input name="word" type="text">  
  <input value="Go" type="button" onclick='JavaScript:xmlhttpPost("/cgi-bin/simple-ajax-example.cgi")'></p>
  <div id="result"></div>
</form>
</body>
</html>

CGI Script

This is the CGI script that the JavaScript in the HTML page calls. This CGI script could just as easily be written in Python, Ruby, PHP etc.

#!/usr/bin/perl -w
use CGI;

$query = new CGI;

$secretword = $query->param('w');
$remotehost = $query->remote_host();

print $query->header;
print "<p>The secret word is <b>$secretword</b> and your IP is <b>$remotehost</b>.</p>";

More Ajax Reference Material