Mon, 15 Aug 2005

Asynchronous Javascript and XML (AJAX)

The Buzzword of the year. It seems to be on everyone's mouth. Specially since GMail and other Google services started using it. So I jumped on the bandwagon, and wrote my menus using this technique. Totally unnecesary? Definitely. Entertaining? You bet. It turns the dullness of writing webpages into something interesting.

So how does it work? As you connect to the website, an XML Http Request is sent from your browser into a Python cgi. That Python CGI reads the variables and pulls the database table that match the parameters. It then proceeds to generate an XML that ultimately your browser (and the Javascript) parses and feeds to the DOM.

Source: toilet.js

posted at: 20:23 | path: /web

Sat, 13 Aug 2005

Javascript Closures

Closures are one of the most fascinating constructs ever IMHO. Not many people know about their existence, let alone in Javascript. However the knowledge of them can seriously leverage your designs.

So what is a closure? A function that keeps an environment. The best way to explain a closure is with an example, so thats what I will show you.

var globalVariable = 20;

function createClosure(arg)
{
   var env = 10;
   return function(x) { alert ( arg + env + x ); }
}

// main body
ourClosure = createClosure(globalVariable);
globalVariable = 0;
ourClosure(30);          // prints 60
alert(globalVariable); // prints 0 

ourClosure() will return 60 even though we have just set the value of the globalVariable to 0. That is, it keeps the values defined when the closure was created.

alert(globalVariable) will output 0, the current value of globalVariable.

IUnknown

posted at: 03:21 | path: /web