Jiving with Javascript, Part III
By Kevin M. Savetz
Other differences are more technical. JavaScript is object-based--its code uses built-in, extensible objects--but unlike Java, there are no classes or object inheritance. In JavaScript, object references are checked at runtime; in Java, object references must exist upon compilation. In JavaScript, variable data types are not declared, unlike in Java, where they must be declared before use.
Which language is better? Until a JavaScript interpreter is complete, there is no fair comparison. Although it was originally intended as a tool for fledgling programmers, even experienced programmers who know Java will find JavaScript useful. The languages can work together to complement each other.
Hurry Up and Wait
Currently, the only Web browser with any support for JavaScript is Netscape 2.0, and it lacks much of the functionality promised for the final release. More than 30 other companies, including Microsoft, have agreed to include support for JavaScript in their Web browsers. With the current version of JavaScript, you can send information to the browser (such as a dialog box) and get the status of objects (such as mouse movements), but some of the most exciting functions, such as the ability to read input streams from documents and to interact with Java applets, remain unimplemented.
When JavaScript includes all the tools the specs say will be included, the two languages will be a mighty team. "As soon as the applet object is released, you will be able to control Java applets with JavaScript, and that will make them work perfectly together," Augustine says. This means that you will be able to control a Java applet using a Web-based form, with a JavaScript doing the behind-the-scenes translation between the Web page and the applet. The user will be able to use a radio button to select how a Java applet will run--for instance, by changing the color and speed of a rotating logo. JavaScript will pass information from the form to the Java applet. JavaScript's applet object will also allow scripts to exchange information with other scripts and CGI programs.
Another tool that will be available in the final release of JavaScript is the "history object," which will allow the script to see what Web pages the user has recently visited (although to protect the user's privacy, the script will not be able to share that information with the server). This would allow a page to offer an intelligent "back" button, letting the user move quickly back to any previously visited Web page.
As with Java, security in JavaScript is likely to be an ongoing battle. Several security problems were quickly discovered in JavaScript 2, including a bug that let JavaScript send a blank electronic mail message to someone without the sender's knowledge. Another bug allowed JavaScript to get a listing of files on the user's hard drive (although the script could not read the contents of any files).
[Move on the Part IV]
Reprinted from Web Developer® magazine, Vol. 2 No. 2 Spring 1996 (c) 1996 internet.com Corporation. All rights reserved.
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