You are reading the comp.lang.javascript meta-FAQ, version 7.5
This is the official comp.lang.javascript (clj) FAQ. Or, more accurately, the meta-FAQ as it mainly provides URLs to further information about javascript and some hints and tips to make your stay in comp.lang.javascript more enjoyable.
This document was created to help reduce the high levels of noise on clj and to provide a resource for people new to javascript or who want to know locations of valuable javascript resources.
The FAQ will currently be posted in two parts, one part (the Quick Answers) on Mondays and Fridays, with the remainder posted on wednesdays
It is also available on the web at http://www.jibbering.com/faq/
Conventions used in the HTML version.
If your browser supports CSS, and follows our Suggestions, we use these conventions to denote various things:
Pages linked to from within a blue dashed line were updated since the last publication of the comp.lang.javascript FAQ (2001-11-26). Links contained in a red dotted line were unavailable at the time of publication.
Boxes with a light blue background, contain links to more information on the question discussed. Code samples are given in a yellow background.
comp.lang.javascript is the official Usenet newsgroup dealing with javascript. There are other newsgroups but many of them are not carried by most news feeds. clj is an unmoderated newsgroup.
clj deals with ECMAScript languages, so any questions about JavaScript or JScript are welcome - however the group has a majority of questions about using javascript in a browser, please make it obvious which host you are using javascript in.
Javascript and Java are two completely different languages. Java questions should be asked in one of the comp.lang.java.* newsgroups; they are not appropriate for clj.
Questions dealing with other scripting languages, such as VBScript, PerlScript or CGI scripting are also off-topic, as are HTML-only or CSS-only questions.
Before posting to clj, you should thoroughly read this document. You should also check the resources mentioned in section 3 and the Quick Answers in section 4. Read FYI28/RFC1855 http://www.ietf.org/rfc/rfc1855.txt , on Usenet and/or http://www.jsiinc.com/newsgroup_document.htm . Also you should read all appropriate posts to the clj newsgroup for several days. Most questions come up at least once every other day and people can get annoyed of answering them repeatedly.
Please state your question as clearly and concisely as possible, as this will make it far easier for the other readers of the list to understand your problems and suggest possible solutions. Use the Subject: of your post to indicate the type of problem you have. 'Help!' or 'I hate Netscape!' are not nearly as useful to contributors who do not read every post as 'parseInt(09)!=9'.
Has the same question already been posted that day? - if it has wait to see if the answers to that solve your problem.
Include the script you have been working on (or URL) - indicate the problem spots and/or previous attempts. Try to limit the length of your post by removing extraneous page elements, but avoid removing script unless you are sure it is not an issue. If the script is long though, please do not post the full script and just provide a link, as a guide more than 500 lines for a post is not normally a good idea in any circumstances. A mention of which platforms and browsers in use or giving problems is also necessary.
Post in plain-text only. Do not post using HTML. If you have to include your script, paste it in to your post in plain-text, do not uuencode it or attach it using mime. There is good reason for this request. Many newsreaders do not read html or mime, and this limits the number of people who could help you. Before a reply, quote only the minimum that needs to be quoted, and add your comments below the quoted material, as FYI28/RFC1855.
Don't ask, or at least expect, to be emailed individually. Some individuals run scams for the purpose of collecting active email addresses and many won't risk being victimized. If you have circumstances that won't allow you to read clj for the follow-up, explain what they are and ask to be CC'ed a copy. You also might try http://groups.google.com/ to read replies.
Don't take flames too seriously. And don't start a thread complaining about rude or flippant responses, there is already enough noise in clj. Keep a sense of humour while posting and reading and everything will be a lot more enjoyable.
Remember that it is not the job of posters here to help you, that the majority of regular posters here do so voluntarily in their free time. They have good days and bad days just like everyone else.
clj is a technical group, postings of job adverts and commercial adverts are not welcome - job postings should go to an appropriate regional jobs group. Announcements of products of particular relevance to javascript are welcome, but not more often than once per major release - then post a short link to your products webpage.
This could be for several reasons:
If it's not one of these, then after a few days consider reposting after checking http://groups.google.com/ for replies. Make sure the post is phrased well, and everything needed to answer is correct, and the subject is appropriate.
This document is posted to clj very frequently. There should be no reason to direct someone to it. However, if someone asks a question answered in this FAQ or in one of the resources listed herein, please let them know their question is answered in the FAQ and that the FAQ can be found at http://www.jibbering.com/faq/
http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM ECMAScript is the international standard for javascript. JScript 3.0 and JavaScript 1.2 (available with version 4. browsers) are more or less ECMAScript compliant. Note that ECMAScript did not attempt to standardize the document object model.
The current edition is Edition 3.0, There is some support for this edition in JScript 5.0 and JavaScript 1.3, JScript 5.5 is compliant, and JavaScript 1.5 available in Netscape 6.1 and later is compliant (Netscape 6 JavaScript 1.5 missed some methods.)
JScript is Microsoft's implementation of ECMAScript.
Object models (OMs) are not part of the javascript language, they are provided by the host to allow javascript (or other scripting language) to communicate with the host. An object model may allow a javascript to access a file system, or control a nuclear power station. The most commonly used object models via javascript are provided by Active Server Pages, Server Side JavaScript, and the Windows Script Host. The most common of all of course is the Document Object Model (DOM) provided by web browsers.
This is the collection of objects provided by each browser. Basically, any object in the window hierarchy is part of the DOM. This means that document.writeln(), for example, is not a javascript method but is, in fact, a method provided by the DOM. The DOM has been standardised by the w3 consortium; however, like all w3 standards, browser support unfortunately is not there yet. Most cross-browser coding problems come from slightly different implementations of the DOM in the different browsers. W3 DOM FAQ http://www.w3.org/DOM/faq
There is little Internationalisation capability in javascript, the various toString() methods are all implementation dependant, but tend to use UK/US settings. ECMAScript Edition 3.0 has introduced some capability including the toLocaleString() method which should create a string based on the hosts locale. In future versions of javascript it is expected that there will be much more support based on the host's Locale.
http://groups.google.com/ Maintain a usenet archive going back over 5 years.
The ECMAScript Technical commitee is now working on Edition 4, the first implementation of which is likely to be JScript.NET, which is currently available in beta form - it includes a compiler, allowing you to create standalone JScript executables.
Edition 4.0 of ECMAScript provides new features like typed variables, classes, other information can be found at: http://www.mozilla.org/js/language/es4/index.html , http://msdn.microsoft.com/voices/scripting07142000.asp or from microsoft.public.dotnet.languages.jscript
There are rather a lot of javascript books available, and if anyone has an example of an up to date good javascript book, I'll gladly add it to the faq.
Javascript FAQ sites, please check these first:
http://www.irt.org/script/faq.htm
http://javascript.faqts.com/
Index of docs online and for download:
http://docs.iplanet.com/docs/manuals/javascript.html
Microsoft (D)HTML reference:
http://msdn.microsoft.com/workshop/author/dhtml/reference/dhtmlrefs.asp
or anonymous FTP of these 2 files:
ftp://ftp.microsoft.com/developr/platformsdk/feb2001/common/help/inet.chm
ftp://ftp.microsoft.com/developr/platformsdk/feb2001/common/help/inet.chi
JScript reference and main Microsoft script site:
http://msdn.microsoft.com/library/en-us/script56/html/js56jsoriJScript.asp
http://msdn.microsoft.com/scripting/
Opera Documentation
http://www.opera.com/docs/specs/#ecmascript
http://www.opera.com/docs/specs/js/
ICab's Inscript documentation
http://www.muchsoft.com/inscript/
Archived documentation for MSIE 3.x:
http://members.tripod.com/~housten/download/
The official ECMAScript specification:
http://www.ecma.ch/ecma1/STAND/ECMA-262.HTM
DOM level 1 ECMA script binding:
http://www.w3.org/TR/REC-DOM-Level-1/ecma-script-language-binding.html
FESI - a free implementation of ECMAScript in Java:
http://home.worldcom.ch/~jmlugrin/fesi/index.html
Frequently asked questions about source code obfuscation:
http://ugweb.cs.ualberta.ca/~thompson/programming/javascript/protect.html
Sites discussing Active Server Pages:
http://www.15seconds.com/
http://www.4guysfromrolla.com/
http://www.aspfaq.com/
DHTML source code and tutorials to a high standard:
http://www.dansteinman.com/dynduo/
http://www.w3schools.com/
Sites focused on using Scripting to automate Windows:
http://www.windows-script.com/
http://cwashington.netreach.net/
Code for manipulating times and dates in javascript:
http://www.merlyn.demon.co.uk/js-dates.htm
Games written in javascript:
http://www.javascript-games.org/
Venkman - Mozilla Visual JS debugger
http://www.mozilla.org/projects/venkman/
Whitebeam Apache Module - Server Side Javascript in Apache
http://www.whitebeam.org/
In the main you don't, as the language is ran from source, you need to deliver the source code, with JScript, there is the Script Encoder (see MSDN) but this is nothing more than obfuscation in effect, disabling the Right Mouse button, also achieves nothing to protect your script in a web browser.
You can't. The browser's history cannot be modified. You can
however use
location.replace(url)
in some browsers to replace the
current page in the history.
Security means that by default you can't. In a more restricted enviroment, there are options (e.g. live connect to Java in NN, and using FileSystemObject in IE) check http://groups.google.com/ for previous posts on the subject.
Writing a cookie, reading it back and checking if it's the same.
In practice you can't, Whilst you could create a suitable encryption system with a password in the page, the level of support you need to do this means it's always simpler to do it serverside. Anything that "protects" a page other than the current one is definitely flawed
In ECMAScript Ed. 3.0 (JScript 5.5 (but buggy)/JavaScript 1.5)
num.toFixed(2)
or for previous versions
Math.round(num*100)/100
, (doesn't add trailing zeros.)
Adding trailing zeros is more complicated to achieve without failing for some numbers. The below works successfully:
function Stretch(Q, L, c) { var S = Q
if (c.length>0) while (S.length<L) { S = c+S }
return S
}
function StrU(X, M, N) { // X>=0.0
var T, S=new String(Math.round(X*Number("1e"+N)))
if (S.search && S.search(/\D/)!=-1) { return ''+X }
with (new String(Stretch(S, M+N, '0')))
return substring(0, T=(length-N)) + '.' + substring(T)
}
function Sign(X) { return X<0 ? '-' : ''; }
function StrS(X, M, N) { return Sign(X)+StrU(Math.abs(X), M, N) }
Number.prototype.toFixed= new Function('n','return StrS(this,1,n)')
Javascript numbers are represented in binary as IEEE-754 Doubles, with a resolution of 53 bits, giving an accuracy of 15-16 decimal digits; integers up to about 9e15 are precise, but few decimal fractions are. Given this, arithmetic is as exact as possible, but no more. Operations on integers are exact if the true result and all intermediates are integers within that range.
In particular, non-integer results should not normally be compared for equality; and non-integer computed results generally need rounding; see 4.6.
To reference another frame, you simply need to step through the
frame hierarchy, parent is the page the frame is defined in,
parent.framename is another frame in the same frameset as the
frame you are in. So to access a variable called Moomin in a
frame called Snork that is in the same frameset you're in you
would use
parent.Snork.Moomin
, to call the function
Snufkin in that frame you would use
parent.Snork.Snufkin()
.
Where supported in NN: (>NN4.0)
var winWidth = window.innerWidth; var winHeight = window.innerHeight;
Where supported in IE: (>IE4.0)
var winWidth = document.body.clientWidth; var winHeight = document.body.clientHeight;
When using IE6 with a DOCTYPE:
var winWidth = document.documentElement.clientWidth var winHeight = document.documentElement.clientHeight
Combined:
d=document
if (typeof window.innerWidth!='undefined') {
var winWidth = window.innerWidth;
var winHeight = window.innerHeight;
} else {
if (d.documentElement &&
typeof d.documentElement.clientWidth!='undefined' &&
d.documentElement.clientWidth!=0) {
var winWidth = d.documentElement.clientWidth
var winHeight = d.documentElement.clientHeight
} else {
if (d.body &&
typeof d.body.clientWidth!='undefined') {
var winWidth = d.body.clientWidth
var winHeight = d.body.clientHeight
}
}
}
var myWin=null;
function openWin(aURL) {
if (!myWin || myWin.closed ) {
myWin=window.open(aURL,'myWin');
} else{
myWin.location=aURL;
myWin.focus();
}
}
IE prints the frame that has focus when you call the print method
frameref.focus();frameref.print();
parseInt decides what base the number is by looking at the
number. By convention it assumes any number beginning with 0 is
Octal, and any number beginning with 0x Hexadecimal. To force
use of base 10 add a second parameter
parseInt(09,10)
el=document.forms['formname'].elements['elementname']; value=el.options[el.selectedIndex].value;
The script
windowref.close();
windowref is window,
or self, top, parent, or a reference obtained when opening the
window, you can only close windows opened by script, no others.
At its simplest in current DOM2 (with innerHTML extension) (IE5+
NS6 ) then having HTML of
<div id="aID">Some
Content</div>
with script of
document.getElementById("aID").innerHTML="Some
<em>new</em> Content";
works.
It is possible though in IE 4+, NS 4+. Code like below achieves
it, but not without many problems in more complicated situations
than described. Be careful - HTML:
<div
ID=aID><layer name='NS_aID';>Some
Content</layer></div>
and
script
DynWrite('aID',"Some
<em>new</em> Content")
With
the below code also in the page:
DocDom = (document.getElementById?true:false);
DocLay = (document.layers?true:false);
DocAll = (document.all?true:false);
DocStr=''
if (DocLay) DocStr="return document.layers['NS_'+id]"
if (DocAll) DocStr="return document.all[id]"
if (DocDom) DocStr="return document.getElementById(id)"
GetRef=new Function("id", DocStr)
if (DocStr=='') { DynWrite=new Function("return false") } else {
if (DocAll || DocDom) {
DynWrite=new Function("id", "S", "GetRef(id).innerHTML=S; return true")
}
if (DocLay) DynWrite=new Function("id", "S", "var x=GetRef(id).document;"+
"x.open('text/html'); x.write(S); x.close(); return true")
}
Using Regular Expressions (JavaScript 1.2/JScript 4+) :
String.prototype.LTrim=new Function("return this.replace(/^\\s+/,'')")
String.prototype.RTrim=new Function("return this.replace(/\\s+$/,'')")
String.prototype.Trim=
new Function("return this.replace(/^\\s+|\\s+$/,'')")
or for all versions (trims characters ASCII<32 not true "whitespace"):
function LTrim(str) {
for (var i=0; str.charAt(i)<=" "; i++);
return str.substring(i,str.length);
}
function RTrim(str) {
for (var i=str.length-1; str.charAt(i)<=" "; i--);
return str.substring(0,i+1);
}
function Trim(str) {
return LTrim(RTrim(str));
}
To reload a page, location.reload() works, however this does
depend on the cache headers that your server sends, to change
this you need to change your server - a quick fix to this on the
client side is to change the URI of the page so it contains a
unique element such as the current
date.
location.replace(location.href+'?d='+new
Date().valueOf())
of if the location.href already
contains a Query String
location.replace(location.href+'&d='+new
Date().valueOf())
You have the serverside language generate the javascript:
jsvar="<%= aspvar %>"; jsvar="<?php echo $phpvar ?>";
etc. For communication between client and server, after a page has loaded, there are a number of "Remote Scripting" options available:
In the normal browser security it is impossible for a script from one domain to access properties of pages served from another domain or by a different protocol, and any attempt by your script to access a property of a window in a different domain will result in a permission denied error. Signed scripts, or trusted ActiveX's can overcome this in limited situations.
There is no ability to cause a delay in javascript, host Object
Models usually provide something. In the browser, there is
window.setTimeout
which can be used to create a delay.
To call the function
Snork()
, approx 10 seconds
after the function
Moomin()
, you would do this:
Moomin()
setTimeout('Snork()',10000)
Script execution is not stopped, and adding
Snufkin()
after the setTimeout line would
immediately execute the function
Snufkin()
before
Snork()
Other hosts have different wait functions such as Windows Script
Hosts
WScript.Sleep()
Javascript variables are loosely typed, and conversion between
Strings and Numbers happen freely, since + is also used for
String concatenation,
"1"+1
is equal to
11
- the String deciding what + does, to overcome
this convert the String to a number:
Number("1")
or
"1"*1
or
"1"-0
or
parseInt("1")
or
parseFloat("1")
or
+varname
. Prompt and Form element values are
all Strings, so convert them to numbers before performing
addition.
function Random(x) { return Math.floor(x*Math.random()) }
gives a random number between 0..(x-1);
Random(N)+1
for [1..N]
In a normal security enviroment, you can't change anything. The page stylesheet rules provide some options, but are not supported in browsers yet. If you can, use an ActiveX or Plugin ScriptX and Neptune from Meadroid to give you more control for Windows versions of Internet Explorer and Netscape 4,6 and Opera 5.
Whatever the rest of your question, this is generally a very bad
use of the javascript pseudo protocol. It was designed to be a
method that a javascript function could return the new page e.g.
javascript:return "<p>Hello</p>"
To use
it simply to call a function, which you then return false from,
causes user agents which do not understand javascript, or have
it disabled, to get nothing other than an error.
<a
href="something.html" onclick="somefunction();return
false">
where something.html is meaningful to the
non-javascript capable, is nearly always preferable. Or use
onclick on another element so users without javascript aren't
even led to believe it does anything.
Form elements with any "illegal" characters can be accessed with
formref.elements["myselect[]"]
- These characters
are illegal in the standard (x)HTML doctypes, so you should try
to avoid them as browsers may perform incorrectly though.
The
navigator
object contains strings which
specify the browser and version; however, this is in general not
very genuine. Mozilla (and therefore Netscape 6) allows this to
be freely set, and Opera and IE allow it to be modified. There
are also at least 25 other javascript capable browsers with
their own strings here.
Generally though, you don't need to identify which browser is being used. There are alternative techniques which depend on why you want to redirect browsers - if it's to offer different CSS stylesheets, then http://pixels.pixelpark.com/~koch/hide_css_from_browsers/ shows many techniques. For Scripting, Object or Feature detection is a better method to use.
Object Detection means checking that the object you wish to use is supported by the browser before using it. This means that you don't need to know what browsers support what methods, and your code will automatically be usable on any browser that can execute it.
if (document.getElementById &&
document.getElementById('el') &&
document.getElementById('el').style ) {
// We know that this browser supports getElementByID and has
// a style object, so we can set a style property.
document.getElementById('el').style.color="red";
}
Browser bugs can often be detected and overcome in similar ways.
The event oncontextmenu of HTML attributes in IE and Mozilla, is the only
reliable and safe method of blocking the context menu, the other
approaches often presented, rarely work, and rely on alert boxes
coming up and even then are limited in their scope:
<body oncontextmenu="return false">
If you have any suggestions for the FAQ, or further questions that you feel should be answered here, please e-mail me at jim@jibbering.com .
The FAQ uses the stylesheet faq.css and is generated from the xml source index.xml by the windows script host script process.wsf which also checks the links.