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Current Bugs and Future Enhancements
This appendix summarizes some of the current "bugs" in JavaScript that you should be aware of and lists a few of the new features hinted at by Netscape in future releases of Netscape Navigator. By the time you have this book in your hands many of these bugs may indeed be fixed (as well as new ones discovered), but you will be able to gain some insight into why JavaScript behaves as it does in your version.

Bugs in JavaScript

Before addressing the new features targeted for release in Netscape Navigator 2.1 and 3.0, lets look at some of the items that represent current bugs in Netscape's JavaScript. These are presented here to help you avoid hours of head scratching and recoding, only to find out that it's not really your fault. To find out if these have been fixed in your version of Netscape, go to the Release Notes section in Navigator..In Windows, select Release Notes from the Help menu; in Macintosh, select Release Notes from the Balloon Help menu. The following items are a few of the current bugs in Netscape's 2.01 version of JavaScript, and ways to avoid them:

onLoad event handler loads prematurely-The onLoad event handler may get called before it is supposed to when you use pages without frames. To work around this, use window.setTimeout() to test for the existance of form elements in your page before running the script you intended for the onLoad event.
Unterminated String Literal error message-This occurs when you try to assign a very long string to a text value. For example:

Listing E.1 Long Strings literals in JavaScript

var thisString="Wow this is a long string of code which will not work in current versions of Netscape!

Especially Windows 3.1. Wow this is a long string of code which will not work in current versions of Netscape!

Especially Windows 3.1. Wow this is a long string of code which will not work in current versions of Netscape!

Especially Windows 3.1. Wow this is a long string of code which will not work in current versions of

Netscape! Especially Windows 3.1."

To fix this, break the string into smaller pieces and concatenate them together using the plus operator (+).
Eval() crashes Navigator in Windows 3.11-This is a known bug and the next version should take care of this. In the mean time, avoid using eval() or check the appVersion (for example, navigator.appVersion) of the client machine and direct them around this code if it is being run on Windows 3.11.
window.open() only opens an empty window-In Macintosh and X versions of Navigator you have to send the window.open() message twice for the information to be passed to the window. If you only send it once, you get a blank open widow. This bug should be fixed in 2.1.
Opening a new window in some X platforms ignores Boolean options-When you open a window you can specify items such as toolbar=yes, and so on. Some versions of Navigator for X ignore this. You should always specify the options for the window.open() method to avoid this problem. Look for a fix in 2.1.
Height and width in IMAGE tags-You should always include HEIGHT and WIDTH attributes on all your images to avoid this bug where event handlers might be ignored on form elements below the images. Another less elegant workaround is to add an empty <SCRIPT>...</SCRIPT> tag to the bottom of that page.
lastIndexOf searching-Normally, the lastIndexOf method should start searching right to left based on the position you specified in the fromIndex value. As of now, it starts one character to the right of that position.
method property of a form object-Right now this property is read only (in 2.01) but you should be able to reset the value of this property in your scripts. Look for a fix in 2.1.
document.close()-If you call document.close() while a document you opened is still loading, it causes Navigator to crash. Check to make sure the document has completely loaded before you call document.close().
name property of object and order of creation-When you give the same name to multiple objects in a form, JavaScript is supposed to create an array with each of those objects in order of creation. If you don't specify an event handler with this object, the indexing will be in reverse of the creation order. This bug shows up most often when you use radio buttons in a form. You should add an event handler to each element (even if the event handler does nothing) in order for them to be indexed correctly.
window.status property-If you check the window.status property, it is always the value of window.defaultStatus. What it should actually be is the current value of this window's status bar instead of a constant value. This will be fixed in an upcoming version to reflect the current status instead.
window.open() and spaces in names-Calling a window.open with a name containing spaces doesn't work, but doesn't call an error message. For example:

window.open("", "Hi There")

simply does not work; nor does it give you an error message. Always check that you don't use spaces. The fix in 2.1 will give you an error message.
SCRIPT tags inside table cells SCRIPT tags inside table cells that write some HTML don't work in 2.0-the HTML is written twice, and the first output is misinterpreted as if it were JavaScript within the SCRIPT tag, during the second pass. To work around this, invert things so your SCRIPT tag writes the table cell markup and the generated HTML (document.lastModified), as follows:

<TABLE WIDTH=100%><TR>

<SCRIPT LANGUAGE="JavaScript">

  document.write("<TD>", document.lastModified, "</TD>")

</SCRIPT>

</TR></TABLE>

Math.random()-Currently, this only works on some X platforms. It is to be fixed in 2.1.
onMouseOver in Navigator Gold in Windows-Currently not working. Look for a fix in the next release of Navigator Gold.
inter-frame and inter-window string and object references-When you reference a string or an object across frames or windows, the value can get corrupted. You should instead assign the "remote" value (the one in the other frame or window) to a new "local" variable. Also, in the instance of strings, you should pre-append a "" to the new value to make sure JavaScript reads the value as a string. For example:

var mystr = "" + parent.otherFrame.stringProperty

You should also avoid passing objects between frames and windows until Netscape version 3.0, which should correct this corruption problem.

Permanent Limitations

JavaScript has certain limitations built in that most likely will not change over time. These limitations are tied closely with the issues of security. Although JavaScript will execute small "programs" on your machine, you do not want it to send or receive information that you do not explicitly request.

JavaScript will most likely never be able to directly write to a file (although recently a script was developed that allows JavaScript to prompt you to save some data in a file of your choice-much like when you download an unknown file type). It hopefully will not be able to access your personal history files (as in sending them to others). It will not access your e-mail address (again, as in sending it to another site).

Also, it will probably, in the future, check a site against some list you develop (or via some RSA security key) and mark a site as "trusted" or "not trusted" and treat that script accordingly. Scripts from trusted sites will probably have greater freedom to manipulate information for you, as well as perform tasks that untrusted sites would be banned from. There is also a new concept called information tainting that will allow scripts to access more sensitive information from your browser; but if it moves outside of a certain scope it will become tainted and the script will be unable to send that information out to some untrusted source.

New Features in JavaScript

Brendan Eich, the engineer at Netscape in charge of JavaScript, has been working to improve JavaScript with each version of Netscape that is released. Because of time constraints, many features originally targeted for the first relase have been delayed. The following section represents some of the features that will be included in future releases of JavaScript.

Netscape Navigator 2.1

Netscape Navigator 2.1 is the next release of the browser to include new features and bug fixes. This release is expected some time in the summer of '96 (as of this writing). This release represents mainly a set of minor changes and improvements over 2.01.

If you read the bug listings earlier in this appendix, you know much about what will be fixed in 2.01. There are a number of items, though, that are not considered bugs, which are also intended to be added to the next version of JavaScript (via the next version of Navigator-since there is no distinction in terms of versioning). The following lists some of these features:

onMouseOver for imagemaps-Currently you cannot use the onMouseOver event handler to control different actions using a client-side imagemap. If you place onMouseOver events in each tag that specifies an area, the Navigator ignores the tag. In 2.1, you should be able to trigger events using a client-side imagemap. For example, the original map:

Listing D.2 Client-Side Imagemap-Before JavaScript

<MAP NAME=bottom>

<AREA SHAPE=rect COORDS="0,0, 46,31" HREF=/search/index.html>

<AREA SHAPE=rect COORDS="47,0, 106,31" HREF=/ads/index.html>

<AREA SHAPE=rect COORDS="107,0, 163,31" HREF=/misc/contact_info.html>

<AREA SHAPE=rect COORDS= "164,0, 223,31"

      HREF="http://merchant.netscape.com/netstore/index.html">

<AREA SHAPE=rect COORDS= "224,0, 285,31" HREF=/toc.html>

<AREA SHAPE=rect COORDS= "286,0, 354,31" HREF=/comprod/mirror/index.html>

<AREA SHAPE=rect COORDS= "355,0, 418,31" HREF=/escapes/galleria.html>

<AREA SHAPE=rect COORDS= "419,0, 468,31"  HREF=/feedback/index.html>

<AREA SHAPE=default  HREF=/index.html>

</MAP>

Using onMouseOver you can add to an area an event to be triggered when a user passes his mouse over that area specified, as follows:

<AREA SHAPE=rect COORDS="0,0, 46,31" HREF=/search/index.html onMouseOver="alert("hi!")>

Currently, if you want events to be triggered by an imagemap, you must use the javascript: URL tag in an HREF link. For example, the preceding line would read as follows:

<AREA SHAPE=rect COORDS="0,0, 46,31" HREF="javascript:alert(Ôhi!Õ)">

The limitation to this is that the user must click that area in order for the script to be executed.
Security fixes-There are many security issues that will be addressed in the next version of Navigator. See the next section, "On Security," for more information about security issues surrounding using JavaScript. In 2.1, JavaScript will have much of the same limitations that Java currently has in terms of writing to the user's local machine, or getting personal information from the client back to the server-such as -mail addresses or listings of files.
Overall stability-You may notice that JavaScript crashes your machine, or brings up an Out of memory error on a page using a clock or some other constantly running script. This is primarily due to the machine not freeing up memory as it is finished (especially with recursive calls to setTimeout()), and will be fixed in 2.1.

Netscape Navigator 3.0

The 3.0 release of Netscape Navigator will include a host of new features in addition to improvements of JavaScript. For instance, it will use Collabra Share, video and audio streaming, Live3D (VRML), and a 2nd generation Java engine. The following is a short listing of the expected changes to JavaScript that have been announced through various channels via the Internet:

Regular expressions-Many scripting languages use a feature called regular expressions. Regular expressions are a set of characters that follow certain rules to match characters in a string. What this means to the JavaScript programmer is that you will be able to search for text based on rules like "Find all five character strings that begin with C and end with ch."
Languages like Perl take great advantage of this ability to parse through submissions of forms via the Web. There will probably be a whole new set of statements for this capability, such as a find() method or a regex() method.
Printing-When a user retrieves a Web page that contains JavaScript that generates HTML on-the-fly in some way (such as saying "Good Evening" at night using the Date object), he currently cannot print the page in the same way that it is displayed on the browser. Instead, the page is printed with blank areas where the generated HTML should have been, or the source code appears (if the page programmer did not use the comment tags to hide the code). This is because of the way the Navigator stores the information that it uses to create the page. Essentially, when a page is printed, it is reread by the browser and converted to the correct code to be sent to the printer. Unfortunately, this interpreter does not recognize JavaScript code. It's as if your browser is of two minds-the new browser which understands the JavaScript elements and the older browser which ignores the commands. In this release, you should be able to print source pages as "generated source" or just "source."
SRC tag-When JavaScript was originally released, it listed the SCRIPT tag as having an attribute called SRC. For example:

<SCRIPT SRC="http://www.mysite.com/foo/scripts/hello.js">

</SCRIPT>

In the 3.0 release, you will be able to hide the source code of your scripts using this SRC tag. It operates much like it would for the IMG tag. Your JavaScript code is written in a file that has a .js extension which you then can reference from anywhere on your pages without having to relist the code over and over again across pages. What is interesting about this new attribute is that it not only will allow you to modularize your JavaScript code, but all of your HTML code. For instance, if you had a page that looked like the following:

Listing D.3 Simple HTML Example

<HTML>

<HEAD>

<TITLE>Welcome to my Site!</TITLE>

</HEAD>

<body background="../../webpages/bookbkg.gif">

<H1>TodayÕs Date is July 14, 1996!</H1>

Welcome.....blah blah

<address>my@address.com</address>

</body background="../../webpages/bookbkg.gif">

</HTML>

Using the new SRC attribute in the SCRIPT tag, you can pull out all of the parts of a page that are reused across your Web site and just point to them from inside a <SCRIPT SCR="">. Listing D.4 is the small page converted to a series of scripts.

Listing D.4 Alternative Code Using JavaScript SRC Attribute

<HTML>

<HEAD>

<SCRIPT SRC="mytitle.js"><SCRIPT>

</HEAD>

<body background="../../webpages/bookbkg.gif">

<SCRIPT SRC="todaysdate.js"></SCRIPT>

<SCRIPT SRC="myintromessage.js"></SCRIPT>

<SCRIPT SRC="myaddress.js"></SCRIPT>

</body background="../../webpages/bookbkg.gif">

</HTML>

This might not seem to save much space at first, but imagine that you have 200 Web pages, and all of them have your address at the bottom. Today you get a new e-mail address. You now have to change your address on 200 pages. Perhaps you know enough UNIX to globally change your pages, or perhaps you have a script that might do that as well, but if you don't, you will be editing your pages for a long time.
With JavaScript, all you will have to do is change the myaddress.js file and all of the pages will reflect this new change. In addition, you can edit your myaddress.jsfile to point itself to myname.js, which appends your name to the end of your address. What this really means is that you will be able to dramatically modularize your pages.

Communicating with Other Elements in the Navigator

As with the SRC tag, the JavaScript documentation originally talked about using JavaScript to read and write properties of plug-ins and Java applets from within the JavaScript script. This specification has yet to be completely hashed out, but you will soon be able to see the properties of applets and plug-ins. There will be two new Navigator properties: navigator.plugins (an array of plug-ins that specify all of the currently registered plug-ins) and navigator.mimeTypes (which specify information about all of the MIME types supported by that Navigator). Later there will also be document.plugins which reflect the information listed in all of the EMBED tags of a given page.

It's expected that you will also have something like navigator.applets, that will correspond to the APPLET tag listings. To get or change attributes of these new properties you will use navigator.plugins[0].propertys[0], or something close to that.

The Future

JavaScript has a bright future if it can keep up with the rapid pace of change that has been the norm for the past few years in the software and Internet development world. JavaScript is relatively robust, useful, and adds a new dimension of interactivity to the Web. There has been a general trend in the computer industry to pass more and more work off to the client machine, which now has the processing power to handle it. JavaScript continues this trend by allowing you to avoid using CGIs for many tasks. And with the development of server-side JavaScript, Web sites will probably become more and more like full blown applications-instead of their current relatively static nature.

BACK TO 100 examples in Business, Operations and Engineering. Click Here	Apply Worldwide Now
Do it once, do it right, and do it now.	Email Lawson Computing
Back to Lawson Computing Homepage	Apply as needed, when needed.

Do it once, do it right, and do it now.

Back to Lawson Computing Homepage