TweetFollow Us on Twitter

Javascript Intro
Volume Number:12
Issue Number:7
Column Tag:Javatech™

Getting the Jump on JavaScript

Start learning to add life to your Web pages

By Kevin M. Savetz

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

Static Web pages are a dying breed. Although not obsolete yet, it may be one day soon that a Web page that doesn’t do anything just won’t get a second glance. Once upon a time, all Web pages were static. CGI programs started to change that by allowing powerful searches of Web pages, sites that modified themselves based on the time of day or the phase of the moon, and even interactive games. Java, a powerful programming language, is bringing a whole new level of interactivity to the Web. Somewhere in the middle is JavaScript, a new language that’s simple enough for beginning programmers to learn, but powerful enough to interact with Web pages and Java applets in ways previously not possible with any language.

JavaScript is a fledgling language. As I write this, JavaScript isn’t even complete. The technical specifications of the language have been agreed upon, but no Web browsers completely support JavaScript. (JavaScript 3.0, which should incorporate the functions that are currently lacking, is due out in June, give or take a month; no firm date had been set at press time.) But that doesn’t mean that no one is using it; bleeding-edge Web hackers have been experimenting with the crippled JavaScript for months, and many are impressed with what they see.

What is JavaScript?

Java and JavaScript are distinct languages, with different purposes and features. JavaScript was designed to provide an easy way for Web authors to create interactive Web pages. Java is a programming language which is used to create stand-alone applications, called applets. Unlike Java, which is meant for experienced programmers with an understanding of C++, JavaScript is a simpler “scripting” language (like dBASE and AppleScript) aimed at those with less programming experience.

Both are powerful languages, but they each offer distinct functionalities. According to Andy Augustine, vice president of technology for Frequency Graphics, a Web development and hosting service provider, “JavaScript is aimed at the people who don’t have C++ experience, people who don’t have much experience with CGI, but want to create some sort of interactive Web page.”

“Contrary to popular misconceptions, JavaScript was not meant to be a scaled-down version of Java, nor was it intended to be a replacement for CGI (server-side) scripts. Instead, JavaScript functions as an outstanding way to enhance both,” he said.

JavaScript can be used to manage user input as well as to show text, play sounds, display images, or communicate with a plug-in in response to “events” such as a mouse-click or exiting or entering a Web page.

JavaScript’s syntax is loosely based on the Java language, but those who have used both languages say the similarity is very loose indeed. In fact, the closest resemblance the two languages have is their names. JavaScript was originally called Mocha while being developed at Netscape. It was later dubbed LiveScript, and when Netscape Communications partnered with Sun to develop Java, LiveScript was renamed JavaScript.

Java vs. JavaScript

JavaScript programs are interpreted and run entirely on the client side. This means fewer hits and less processing time on the server than with Java (where applets are compiled on the server before being executed on the client) or CGI (which requires the server to do the work and rack up hits).

There are other differences between the two languages. In Java, applets are files distinct from HTML pages; with JavaScript, the code is integrated into the HTML using special tags. (This can cause problems with some Web browsers that do not properly handle JavaScript code.) Like Java, JavaScript is a cross-platform language that can work with any compatible browser.

Here’s an example HTML file with an embedded JavaScript. Between the <BODY> tags, the Web browser displays a form with a space to enter a number. When the user enters a number in the field, the browser starts the script, located between the <SCRIPT> tags. The script itself makes sure the user really entered a number, and displays a dialog box if the user didn’t keep the number within pre-defined limits.

<HEAD>
<SCRIPT LANGUAGE="JavaScript">
<!--- these comments should hide the script from old browsers
function checkNum(str, min, max) {
 if (str == "") {
 alert("Enter a number in the field, please.")
 return false
 }
 for (var i = 0; i < str.length; i++) {
 var ch = str.substring(i, i + 1)
 if (ch < "0" || ch > "9") {
 alert("Enter a number, please.")
 return false
 }
 }

 var val = parseInt(str, 10)
 if ((val < min) || (val > max)) {
 alert("Try a number from 1 to 10.")
 return false
 }
 return true
}

function thanks() {
 alert("Thank you.")
}
// end hiding from old browsers -->
</SCRIPT>
</HEAD>

<BODY>
<FORM NAME="ex5">
Please enter a number from 1 to 10:
<INPUT NAME="num"
 onChange="if (!checkNum(this.value, 1, 10))
 {this.focus();this.select();} else {thanks()}">
</FORM>
</BODY>

All this only takes one hit on the server - to download the HTML code and the embedded script. Doing this with a CGI script would require multiple hits on the server, once for the HTML file, and again to verify the input every time the user types into the form. JavaScript allows the client to perform more significant calculations without weighing down the server.

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 run-time; 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.

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 abilities to read input streams from documents and to interact with Java applets, are still unimplemented.

When JavaScript includes all of the tools the specs say will be included, including something called the “applet object” (which will allow scripts to interact with Java applets), 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, 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 send information to and get information from 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).

Now or Later?

Should you bother learning JavaScript now, or is it currently just a toy for experimenters? Should you wait until the final version of the JavaScript interpreter ships before trying to learn the ins and outs of the language? Augustine thinks that now is the time to get a jump start on JavaScripting. “Learn JavaScript right now if you want to capture the market while it is viable; you’ll be ahead of the field. If you wait until it is fully functional before you learn it, I think you’ll be behind the game,” he says. Online tutorials can get you started with the basics of the language, and Internet mailing lists and newsgroups devoted to the topic are already home to thriving communities of developers and experimenters.

Will the serious Web page developer need to understand both Java and JavaScript? Because JavaScript can interact directly with the user anywhere on a Web page (rather than being limited to a single window, as with Java), most Java developers will probably want to learn both. But JavaScript should also be viable as a stand-alone tool for less experienced programmers who want to add interactivity to their Web pages.

Example Scripts

There are already dozens of example JavaScripts on the Web. Many, such as the 1040EZ tax form and body mass calculator, simply compute values input from an HTML form. Others are more inspired, such as the currency exchange calculator, which lets you select two countries from a list and then computes the


exchange rate. I am particularly fond of the Zen koan generator, even though it occasionally causes Netscape 2.0 to crash.

http://www.homepages.com/fun/1040EZ.html

http://www.iohk.com/UserPages/acheng/javascript.html

http://www.superprism.net/doc/EXPRESS/util/currency.html

http://www.wrldpwr.com/javascriptzen.html

The color picker shows how JavaScript can work with frames and color: pass the mouse over the name of a color in one frame and the background of another frame will become that color. Other examples are downright inspirational, such as the JavaScript VRML clock, which uses JavaScript to display a three-dimensional clock if you have a VRML browser.

http://www.lsi.usp.br/doc/color/picker.html

http://www.phoenix.net/~jalonso/applets/vrml

Many more example applications are available at http://www.gamelan.com/.

Remember how interesting (and sometimes annoyingly funky) Web pages became when authors started using and abusing sundry new tools like backgrounds and frames? Expect to see another round of enlightening and obscure Web sites as developers and hackers begin to understand and use JavaScript.

For More Information

A growing number of information sources about JavaScript are online. Andy Augustine’s JavaScript FAQ is at:

http://www.freqgrafx.com/411/jsfaq.html

There is also a JavaScript mailing list, a high-volume, sometimes technical list for discussion about using the language. To subscribe, send a message to majordomo@obscure.org with a message body of “subscribe javascript”. A digest version of the list is also available. To subscribe, use a message body of “subscribe javascript-digest”. Further discussion takes place on the newsgroup comp.lang.javascript.

Netscape’s official JavaScript documentation is required reading if you plan to learn your way around JavaScript. The files are also downloadable for reading offline.

http://home.netscape.com/eng/mozilla/2.0/handbook/javascript/index.html

http://home.netscape.com/eng/mozilla/2.0/handbook/javascript/jsdoc.zip

Augustine maintains a list of online tutorials, example applications and other information at JavaScript 411. Finally, the ubiquitous Yahoo naturally has an index of JavaScript-related goodies.

http://www.freqgrafx.com/411/

http://www.yahoo.com/Computers_and_Internet/Languages/JavaScript/

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Sibelius 2020.6 - Music notation solutio...
Sibelius is the world's best-selling music notation software for Mac. It is as intuitive to use as a pen, yet so powerful that it does most things in less than the blink of an eye. The demo includes... Read more
Bookends 13.4.2 - Reference management a...
Bookends is a full-featured bibliography/reference and information-management system for students and professionals. Bookends uses the cloud to sync reference libraries on all the Macs you use.... Read more
OmniGraffle Pro 7.16 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
Drive Genius 6.1.0 - $79.00
Drive Genius features a comprehensive Malware Scan. Automate your malware protection. Protect your investment from any threat. The Malware Scan is part of the automated DrivePulse utility. DrivePulse... Read more
Tor Browser 9.5 - Anonymize Web browsing...
The Tor Browser Bundle is an easy-to-use portable package of Tor, Vidalia, Torbutton, and a Firefox fork preconfigured to work together out of the box. It contains a modified copy of Firefox that... Read more
VueScan 9.7.28 - Scanner software with a...
VueScan is a scanning program that works with most high-quality flatbed and film scanners to produce scans that have excellent color fidelity and color balance. VueScan is easy to use, and has... Read more
OmniGraffle 7.16 - Create diagrams, flow...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
WALTR 2 2.6.26 - $39.95
WALTR 2 helps you wirelessly drag-and-drop any music, ringtones, videos, PDF, and ePub files onto your iPhone, iPad, or iPod without iTunes. It is the second major version of Softorino's critically-... Read more
Airmail 4.1 - Powerful, minimal email cl...
Airmail is an mail client with fast performance and intuitive interaction. Support for iCloud, MS Exchange, Gmail, Google Apps, IMAP, POP3, Yahoo!, AOL, Outlook.com, Live.com. Airmail was designed... Read more
Iridient Developer 3.3.12 - Powerful ima...
Iridient Developer (was RAW Developer) is a powerful image-conversion application designed specifically for OS X. Iridient Developer gives advanced photographers total control over every aspect of... Read more

Latest Forum Discussions

See All

Willy Jetman: Astromonkey's Revenge...
Barcelona-based developer Last Chicken Games are set to bring their game Willy Jetman: Astromonkey's Revenge to both iOS and Android on 9th July. The Metroidvania is already available on the likes of PS4, Switch and PC but now mobile folk will be... | Read more »
The 5 Best Mobile Real Time Strategy Gam...
Real-time strategy games feel like they’d be a perfect fit for mobile, but they’re trickier to pull off that you might think. The traditional mold of base-building and micro management can work on touch screens, but needs to be carefully honed so... | Read more »
Using your phone in a protest
I can't write about games today. There is a struggle happening in the streets right now and it needs everyone's attention. Here's some good info on how you can use your iOS device safely amidst a protest. | Read more »
Dungonian is a card-based dungeon crawle...
Dungonian is a card-based dungeon crawler from developer SandFish Games that only recently launched as a free-to-play title. It offers an extensive roster of playable heroes to collect and enemies to take down, and it's available right now for iOS... | Read more »
Steam Link Spotlight - Signs of the Sojo...
Steam Link Spotlight is a feature where we look at PC games that play exceptionally well using the Steam Link app. Our last entry was XCOM: Chimera Squad. Read about how it plays using Steam Link's new mouse and keyboard support over here. | Read more »
Steampunk Tower 2, DreamGate's sequ...
Steampunk Tower 2 is a DreamGate's follow up to their previous tower defence game. It's available now for both iOS and Android as a free-to-play title and will see players defending their lone base by kitting it out with a variety of turrets. [... | Read more »
Clash Royale: The Road to Legendary Aren...
Supercell recently celebrated its 10th anniversary and their best title, Clash Royale, is as good as it's ever been. Even for lapsed players, returning to the game is as easy as can be. If you want to join us in picking the game back up, we've put... | Read more »
Pokemon Go Fest 2020 will be a virtual e...
Niantic has announced that Pokemon Go Fest will still take place this year although understandably it won't be a physical event. Instead, it will become a virtual celebration and is set to be held on 25th and 26th July. [Read more] | Read more »
Marvel Future Fight's major May upd...
Marvel Future Fight's latest update has now landed, and it sounds like a big one. The focus this time around is on Marvel's Guardians of the Galaxy, and it introduces all-new characters, quests, and uniforms for players to collect. [Read more] | Read more »
SINoALICE, Yoko Taro and Pokelabo's...
Yoko Taro and developer Pokelabo's SINoALICE has now opened for pre-registration over on the App Store. It's already amassed 1.5 million Android pre-registrations, and it's currently slated to launch on July 1st. [Read more] | Read more »

Price Scanner via MacPrices.net

Apple restocks 27″ iMacs, Certified Refurbish...
Apple has restocked Certified Refurbished 2019 27″ iMacs starting at $1529 and up to $350 off the cost of new models. Apple’s one-year warranty is standard, shipping is free, and each iMac features a... Read more
Apple’s new 2020 13″ 4-Core MacBook Airs on s...
B&H Photo has Apple’s new 2020 13″ 4-Core MacBook Airs on sale today for $100 off Apple’s MSRP, only $1199. Expedited shipping is free to many addresses in the US. The MacBook Airs are the same... Read more
New Verizon promo: $150 off any Apple Watch w...
Verizon is offering $150 off any Apple Watch when purchased alongside an iPhone through June 10, 2020. They’re also offering up to $100 on any Apple Watch trade-in. Here are the details: “Get $150... Read more
Last year’s 13″ 2.4GHz MacBook Pros are avail...
Apple has Certified Refurbished 2019 13″ 2.4GHz/256GB 4-Core Touch Bar MacBook Pros available for $1359, $440 off original MSRP. Apple’s one-year warranty is included, shipping is free, and each... Read more
Apple’s new 2020 13″ MacBook Pros on sale for...
Apple reseller Abt Electronics has new 2020 13″ MacBook Pros on sale today for up to $140 off MSRP, starting at $1208. Shipping is free, and most configurations are in stock today. Note that Abt’s... Read more
Apple CEO Reacts To Nationwide Protests Over...
NEWS: 06.03.20 – With the recent death of a black man in the custody of a white police officer igniting outrage among Americans from all walks of life, which resulted in protests and civil unrest... Read more
At up to $420 off MSRP, these Certified Refur...
Apple has Certified Refurbished 2019 16″ MacBook Pros available for up to $420 off the cost of new models, starting at $2039. Each model features a new outer case, shipping is free, and an Apple 1-... Read more
Apple restocks refurbished 3rd generation 12....
Apple restocked select 3rd generation 12.9″ WiFi iPad Pros starting at only $699 and up to $330 off original MSRP. Each iPad comes with a standard Apple one-year warranty, outer cases are new, and... Read more
These wireless carriers are offering Apple’s...
Looking for a deal on Apple’s new iPhone SE? Apple itself offers the unlocked 64GB iPhone SE for $399 or $16.62/month. If you’re willing to try a new carrier, two of Apple’s wireless carriers are... Read more
Save $80 on the 64GB 10.5″ iPad Air with this...
Apple has 10.5″ 64GB WiFi iPad Airs models available for $80 off MSRP, Certified Refurbished. Each iPad comes with Apple’s standard one-year warranty and includes a new outer case. Shipping is free... Read more

Jobs Board

*Apple* Architect - SAIC (United States)
**Description** We are currently seeking a motivated, career and customer oriented Apple Architect to join our team in Washington, DC to begin an exciting and Read more
*Apple* Support Engineer - SAIC (United Stat...
**Description** We are currently seeking a motivated, career and customer oriented Apple Support Engineer to join our team in Washington, DC to begin an exciting and Read more
Perioperative RN - ( *Apple* Hill Surgical C...
Perioperative RN - ( Apple Hill Surgical Center) Tracking Code 60593 Job Description Monday - Friday - Full Time Days Possible Saturdays General Summary: Under the Read more
Senior Practice Manager - *Apple* Hill Eye...
Senior Practice Manager - Apple Hill Eye Center Tracking Code 61713 Job Description Apple Hill Medical Center General Summary: Under general supervision, manages Read more
*Apple* Mac Desktop Support - Global Dimensi...
…Operate and support an Active Directory (AD) server-client environment for all Apple devices operating on the BUMED network + Leverage necessary industry enterprise Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.