14 June 2005

On a Foray into HTML-3

SunSoft Java[*], and Netscape JavaScript [*] are closely related ideas. They're both programming languages that are commonly associated with the internet. The similar names are just a coincidence, however, and they refer to very different things. In this blog post and others, I'm going to refer to a program and its elements as "code." You could say programs are written with code. I also will use a term, "compiler." This is a program that reads code written in a high-level language and translates it into assembly language so the computer can do what it's supposed to do.

Java was developed about the same time as Mosaic, the first Web browser. Most computers supplied since 1990 have a "Java virtual machine" (JVM) that is a compiler for Java code. This allows Java code to be read by any browser anywhere, any time, regardless of the computer on which one is browsing the web. The VM is common to all browsers, regardless of flavor (this is not STRICTLY true!).

An application is any program that you need a computer for, such as word processing or managing a database. An application written in Java is called an applet. An applet can do pretty much anything that a conventional application can do; so, for example, this list of applets includes calculators, graphers, simulators; an MP3 player; chat rooms, email programs, and spam blockers are also written in Java.
What about JavaScript? JavaScript was created by Netscape as a simple set of commands that all browsers would recognize. Unlike Java, which is a completely separate programming language, designed for autonomous applications, JavaScript is a set of commands recognized by browsers. JavaScript programs, or scripts, are usually embedded directly in HTML files. The script executes when the user's browser opens the HTML file.

JavaScript allows the person visiting your website to interact with the site. A simple script involves letting the visitor select the background color of the page. Another script can detect the user's operating system and browser type, then give instructions that are appropriate to the user's particular computer. A third type evaluates user input. Drop down menus and combination bars are things that you can do with JavaScript.

(To be continued.)

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