JAVASCRIPT

JavaScript Remote Scripting: Reading Data From the Server

Client-server interaction achieved without involving page reloads has become very popular for Web services. This can be handled in a variety of ways. This article covers several of them, starting with Asynchronous JavaScript and XML (AJAX).

Author Info:

By: Alejandro Gervasio

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September 21, 2005

TABLE OF CONTENTS:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>REMOTE SCRIPTING WITH AJAX</title>
<script type="text/javascript">
// initialize XMLHttpRequest object
var xmlobj=null;
// initialize global variables
var data=new Array();
var i=0;

// send http request
function sendRequest(doc){
    // check for existing requests
    if(xmlobj!=null&&xmlobj.readyState!=0&&xmlobj.readyState!=4){
        xmlobj.abort();
    }
    try{
        // instantiate object for Firefox, Nestcape, etc.
        xmlobj=new XMLHttpRequest();
    }
    catch(e){
        try{
            // instantiate object for Internet Explorer
            xmlobj=new ActiveXObject('Microsoft.XMLHTTP');
        }
        catch(e){
            // Ajax is not supported by the browser
            xmlobj=null;
            return false;
        }
    }
    // assign state handler
    xmlobj.onreadystatechange=stateChecker;
    // open socket connection
    xmlobj.open('GET',doc,true);
    // send request
    xmlobj.send(null);
}

// check request status
function stateChecker(){
    // if request is completed
    if(xmlobj.readyState==4){
        // if status == 200 display text file
        if(xmlobj.status==200){
            // create data container
            createDataContainer();
            // display data into container
            data=xmlobj.responseText.split('|');
            displayData();
        }
        else{
            alert('Failed to get response :'+ xmlobj.statusText);
        }
    }
}

// create data container
function createDataContainer(){
    var div=document.createElement('div');
    div.setAttribute('id','container');
    if(div.style){
        div.style.width='500px';
        div.style.height='45px';
        div.style.padding='5px';
        div.style.border='1px solid #00f';
        div.style.font='bold 11px Tahoma,Arial';
        div.style.backgroundColor='#eee';
        document.getElementsByTagName('body')[0].appendChild
(div);
    }
}

// display data at a given time interval
function displayData(){
    if(i==data.length){i=0};
    document.getElementById('container').innerHTML=data[i];
    i++;
    setTimeout('displayData()',20*1000);
}

// execute program when page is loaded
window.onload=function(){
    // check if browser is DOM compatible
    if(document.getElementById &&
       document.getElementsByTagName &&
       document.createElement){
        // load data file
        sendRequest('technews.txt');
    }
}
</script>
</head>
<body>
</body>
</html>

To wrap up

That's all for now. In the second part of this article, I'll explain how to use JavaScript remote scripting for working directly with XML files by using AJAX technology. Also, I'll run through an illustrative example, helpful to implement within many client-side programs. Considering that remote scripting can boost considerably modern Web applications, the topic is worthy of review. See you soon!

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