JavaScript Introduction - Tutorial Tour

JavaScript Introduction

JavaScript Introduction
JavaScript Introduction

JavaScript Introduction : JavaScript is most commonly used as a client side scripting language. This means that JavaScript code is written into an HTML page. When a user requests an HTML page with JavaScript in it, the script is sent to the browser and it’s up to the browser to do something with it. You can use it to check or modify the contents of forms, change images, open new windows and write dynamic page content. You can even use it with CSS to make DHTML (Dynamic HyperText Markup Language). This allows you to make parts of your web pages appear or disappear or move around on the page. JavaScripts only execute on the page(s) that are on your browser window at any set time. When the user stops viewing that page, any scripts that were running on it are immediately stopped. The only exceptions are cookies or various client side storage APIs, which can be used by many pages to store and pass information between them, even after the pages have been closed.

Before we go any further, let me say; JavaScript has nothing to do with Java. If we are honest, JavaScript, originally nicknamed LiveWire and then LiveScript when it was created by Netscape, should in fact be called ECMAscript as it was renamed when Netscape passed it to the ECMA for standardisation.


The JavaScript language : JavaScript is not a programming language in strict sense. Instead, it is a scripting language because it uses the browser to do the dirty work. If you command an image to be replaced by another one, JavaScript tells the browser to go do it. Because the browser actually does the work, you only need to pull some strings by writing some relatively easy lines of code. That’s what makes JavaScript an easy language to start with.

But don’t be fooled by some beginner’s luck: JavaScript can be pretty difficult, too. First of all, despite its simple appearance it is a full fledged programming language: it is possible to write quite complex programs in JavaScript. This is rarely necessary when dealing with web pages, but it is possible. This means that there are some complex programming structures that you’ll only understand after protracted studies.

Secondly, and more importantly, there are the browser differences. Though modern web browsers all support JavaScript, there is no sacred law that says they should support exactly the same JavaScript. A large part of this site is devoted to exploring and explaining these browser differences and finding ways to cope with them.

So basic JavaScript is easy to learn, but when you start writing advanced scripts browser differences (and occasionally syntactic problems) will creep up.

Security : Client–side JavaScript has expressly been developed for use in a web browser in conjunction with HTML pages. This has certain consequences for security.

Programs are passed to the computer that the browser is on, and that computer runs them. The alternative is server side, where the program is run on the server and only the results are passed to the computer that the browser is on. Examples of this would be PHP, Perl, ASP, JSP etc.

Browser incompatibilities : When a user receives a page which includes JavaScript, the JavaScript interpreter of his browser kicks in and tries to execute the script. Now the main problem here is that the various browsers each use their own interpreter, and that sometimes browser vendors have chosen not to implement a bit of JavaScript. Their reasons were usually related to business advantage over the competitors.

Hence the feared browser incompatibilities.

In addition each new browser version understands more JavaScript and allows more and more parts of the HTML page to be changed by scripts. This leads to even more incompatibilities.

It’s best to solve compatibility problems on a case–by–case basis. In fact, most pages on this site have been written precisely because of browser incompatibilities. So read on to understand more. But I warn you: you need to digest quite a lot of information. Therefore it’s best to solve the problem at hand and leave the rest of the information alone until you need it.

JavaScript Introduction


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