You are reading the comp.lang.javascript meta-FAQ, version 9.65. It is available on the web at www.jibbering.com/faq/index.html in HTML form.
This is the official comp.lang.javascript (clj) FAQ. Or, more accurately, the meta-FAQ. 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 for three reasons: to help reduce the high levels of noise on clj, to provide a resource for people new to javascript, and to point to locations that contain valuable javascript resources.
The FAQ is currently posted one section daily for review, questions and a reminder that the FAQ is available.
To cope with a desire for additional explanation and detail relating to some aspects of the FAQ, an additional resource is available at:- www.jibbering.com/faq/faq_notes/faq_notes.html It has been provided separately to avoid increasing the size of the FAQ to a point where it would be unreasonable to post it to the group.
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 (2007-03-04). 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.
The official Usenet newsgroup dealing with javascript is comp.lang.javascript . There are other newsgroups but many of them are not carried by most news feeds. clj is an unmoderated newsgroup.
The comp.lang.javascript newsgroup deals with ECMAScript languages, so any questions about JavaScript or JScript are welcome. However, the majority of questions sent to this group relates to javascript in a web browser. If you are experiencing issues with a particular browser, or the host is not a browser at all, please make this information clear.
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 (as Java and javascript are distinct programming languages with only superficial similarities due to sharing a C-like syntax and some of the characters in their names).
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.
Questions that are specific to Microsoft's JScript may also be appropriately asked at: microsoft.public.scripting.jscript
The comp.lang.javascript newsgroup charter is included in www.jibbering.com/faq/faq_notes/cljs_charter.html
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 www.ietf.org/rfc/rfc1855.txt on Usenet and www.jibbering.com/faq/faq_notes/clj_posts.html . 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 group to understand your problems and suggest possible solutions. Use the Subject: of your post to indicate the type of problem you have, but include the question in the body as well. '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 are used or are 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. Test posts belong in test newsgroups (they have "test" in their names). Make sure your code is executable as transmitted. Use line breaks to keep the posting agent from wrapping code incorrectly.
When replying to a message on the group quote the minimum of the preceding messages that is sufficient to provide context for the reply but trim the remainder, and add your comments below the pertinent section of quoted material, as per FYI28/RFC1855 (never top post).
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 groups.google.com/group/comp.lang.javascript/topics to read replies.
Don't expect to be able to e-mail contributors to the group privately. E-mail addresses are often obscured, fictional or unmonitored spam sinks (this is an increasingly normal (and even unofficially recommended) practice as open e-mail addresses in news articles will be both the target of spam and used as fake sender's addresses in spam to third parties).
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. 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: the posting 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, and then post a short link to the product's webpage.
Please do not post copyrighted material to clj without permission from the copyright holder.
This could be for several reasons:
If it is not one of these, then after a few days consider reposting after checking groups.google.com/group/comp.lang.javascript/topics 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 www.jibbering.com/faq/
www.ecma-international.org/publications/standards/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. In addition ECMA 327 defines the Compact Profile of ECMAScript by describing the features from ECMA 262 that may be omitted in some resource-constrained environments. Note that ECMAScript did not attempt to standardize the document object model.
The current edition is ECMA-262, 3rd Edition. There is some support for this edition in JScript 5.0 and JavaScript 1.3. JScript 5.5 and JavaScript 1.5, in Netscape 6.1 and later, are compliant (JavaScript 1.5 in Netscape 6 missed some methods).
JScript is Microsoft's implementation of ECMAScript.
Questions that are specific to Microsoft's JScript may also be appropriately asked at: microsoft.public.scripting.jscript
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 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. Other document types such as SVG also define scriptable DOMs, mostly as extensions of the W3C Core DOM specification designed for use with XML documnets.
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 World Wide Web Consortium (W3C); however, like all W3C standards, browser support is not yet complete. Most cross-browser coding problems come from slightly different implementations of the DOM in the differentbrowsers. W3 DOM FAQ www.w3.org/DOM/faq.html
The W3C has worked on three versions of the DOM to date. The third version has not yet achieved the status of a recommendation www.w3.org/DOM/ .
Internationalization means using one form which is both acceptable and understood everywhere. By default, javascript has no such features; but if an international standard exists it can be coded for.
For example, there is an international standard for numeric Gregorian date format; but there is none for decimal and thousands separators.
Multinationalization means using different forms for different nations. It cannot work well in general, because it requires a knowledge of all national preferences and the ability to choose the right one, in an environment where many systems are inappropriately set anyway.
JavaScript has a few Multinationalisation features. The various toString() methods are all implementation dependent, but tend to use either UK or US settings (not necessarily correctly). ECMAScript Ed. 3 introduced some capabilities, including the toLocaleString() method which should create a string based on the host's locale.
Much more support is expected in future versions of JavaScript.
groups.google.com/group/comp.lang.javascript/topics Maintain an archive of comp.lang.javascript going back to 1996 and provide diverse archive searching facilities.
The ECMAScript Technical Committee is now working on the fourth edition, the first implementation of which is JScript.NET. It includes a compiler, allowing you to create standalone JScript executables.
The fourth edition of ECMAScript will provide new features like typed variables, and classes. More information can be found at: www.mozilla.org/js/language/es4/index.html , msdn.microsoft.com/voices/scripting07142000.asp or from microsoft.public.dotnet.languages.jscript
The only book currently endorsed by c.l.j. regulars is:
JavaScript: The Definitive Guide, 4th Edition By David Flanagan ISBN:0-596-00048-0
Also by David Flanagan: JavaScript Pocket Reference, 2nd Edition. ISBN 0-596-00411-7 for language and API reference alone.
The Fifth Edition has been released but has not been reviewed thoroughly enough to gain a full endorsement from the regulars of c.l.j.
JavaScript: The Definitive Guide, 5th Edition By David Flanagan ISBN:0-596-10199-6
Javascript FAQ site, please check first:-
javascript.faqts.com/
Mozilla JavaScript 1.5 reference:-
developer.mozilla.org/en/docs/JavaScript
Index of Netscape 4 JavaScript docs online (These documents are no longer available form Netscape but are still reproduced by Sun Microsystems, Inc.):-
docs.sun.com/source/816-6408-10/
Index of Archived Netscape 4 JavaScript docs online and for download:-
devedge-temp.mozilla.org/library/manuals/2000/javascript/1.3/reference/
Online Gecko DOM Reference:-
developer.mozilla.org/en/docs/Gecko_DOM_Reference
Download:-
www.mozilla.org/docs/dom/domref.zip
Microsoft (D)HTML reference:-
msdn.microsoft.com/workshop/author/dhtml/reference/dhtml_reference_entry.asp
JScript reference and main Microsoft script site:-
msdn.microsoft.com/library/en-us/script56/html/1e9b3876-3d38-4fd8-8596-1bbfe2330aa9.asp
msdn.microsoft.com/scripting/
Opera Documentation:-
www.opera.com/docs/specs/#ecmascript
www.opera.com/docs/specs/js/
ICab's Inscript documentation:-
www.muchsoft.com/inscript/
Archived documentation for MSIE 3.x:-
members.tripod.com/~housten/download/
The official ECMAScript specification:-
www.ecma-international.org/publications/standards/Ecma-262.htm
Other versions of the ECMAScript specification:-
www.mozilla.org/js/language/
DOM level 1 ECMA script binding:-
www.w3.org/TR/REC-DOM-Level-1/ecma-script-language-binding.html
DOM HTML level 2 ECMA script binding:-
www.w3.org/TR/DOM-Level-2-HTML/ecma-script-binding.html
FESI - a free implementation of ECMAScript in Java:-
www.lugrin.ch/fesi/index.html
Frequently asked questions about source code obfuscation:-
jibbering.com/faq/obfuscate.html
Sites discussing Active Server Pages:-
www.15seconds.com/
www.4guysfromrolla.com/
www.aspfaq.com/
DHTML source code and tutorials:-
www.w3schools.com/
Sites focused on using Scripting to automate Windows:-
www.windows-script.com/
cwashington.netreach.net/
Microsoft's Windows Scripting Host (WSH) Newsgroup:-
microsoft.public.scripting.wsh
Microsoft's JScript Newsgroup:-
microsoft.public.scripting.jscript
Manipulating times, dates and the lastModified date and time in javascript:-
www.merlyn.demon.co.uk/js-dates.htm
Venkman - Mozilla Visual JS debugger:-
www.mozilla.org/projects/venkman/
Whitebeam Apache Module - Server Side Javascript in Apache;-
www.whitebeam.org/
Digital Mars DMD Script, console and MS Active Script implementation of ECMAScript, claimed to be faster than other implementations:-
www.digitalmars.com/dscript/
Microsoft Script Debugger Documentation:
msdn.microsoft.com/library/en-us/sdbug/Html/sdbug_1.asp
With clientside Javascript you can't as your code is distributed in source form and is easily readable. With JScript, there is the Script Encoder (see MSDN), but this is nothing more than obfuscation. Disabling the right mouse button also does nothing to protect your script in a Web browser.
You can't. The browser's history cannot be modified. However, you
can 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 environment, there are options. For example, using LiveConnect to connect to Java with Netscape, and using the FileSystemObject in IE. Check groups-beta.google.com/group/comp.lang.javascript/topics for previous posts on the subject.
Writing a cookie, reading it back and checking if it's the same.
In practice you can't. While 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 server-side. Anything that "protects" a page other than the current one is definitely flawed.
When formatting money for example, to format 6.57634 to 6.58, 6.5 to 6.50, and 6 to 6.00?
Rounding of x.xx5 is uncertain, as such numbers are not represented exactly. See section 4.7 for Rounding issues.
N = Math.round(N*100)/100 only converts N to a Number of value close to a multiple of 0.01; but document.write(N) does not give trailing zeroes.
ECMAScript Ed. 3.0 (JScript 5.5 [but buggy] and JavaScript 1.5) introduced N.toFixed, the main problem with this is the bugs in JScripts implementation.
Most implementations fail with certain numbers, for example 0.07. The following works successfully for M>0, N>0:
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= function(n){ return StrS(this,1,n)};
Javascript numbers are represented in binary as IEEE-754 (IEC 559) 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.
To access a variable called Moomin in a frame called Snork you
would use
parent.Snork.Moomin
. To call the function Snufkin
in that frame you would use
parent.Snork.Snufkin()
.
While it is often asked about window size, what is more relevant is the "canvas area" of the browser.
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 in CSS1Compat mode (i.e. with a Formal DOCTYPE):
var winWidth = document.documentElement.clientWidth var winHeight = document.documentElement.clientHeight
Combined:
var winWidth, winHeight, d=document;
if (typeof window.innerWidth!='undefined') {
winWidth = window.innerWidth;
winHeight = window.innerHeight;
} else {
if (d.documentElement &&
typeof d.documentElement.clientWidth!='undefined' &&
d.documentElement.clientWidth!=0) {
winWidth = d.documentElement.clientWidth
winHeight = d.documentElement.clientHeight
} else {
if (d.body &&
typeof d.body.clientWidth!='undefined') {
winWidth = d.body.clientWidth
winHeight = d.body.clientHeight
}
}
}
Note: The dimensions can not be determined accurately until after the document has finished loading.
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();
The parseInt function decides what base to
convert a number represented as a string
to by looking at the string. It assumes that
any string beginning with '0x' or '0X' represents
a hexadecimal number, but it has a choice with a
leading zero: the string could represent a number
that can be either octal or decimal. Assuming
octal, the string '09' will be converted to 0
(octal digits are 0-7); assuming decimal, '09'
will be converted to 9 (the leading zero is
ignored). To force use of a particular base,
use the radix parameter:
parseInt("09",base)
In HTML documents, named forms may be referred to as named
properties of the
document.forms
collection, and named form
controls may be referred to as named properties of the form's
elements collection:
var frm = document.forms["formname"]; var contrl = frm.elements["elementname"];
The (string) value property of such controls can be read directly from the element:-
var value = contrl.value; var value = (+contrl.value); //string to number: see 4.21
Some exceptions would be:
First Exception: Where the control is a SELECT element, and support for older browsers, such as NN4, is required:
var value = contrl.options[contrl.selectedIndex].value;
Second Exception: Where several controls share the same name, such as radio buttons. These are made available as collections and require additional handling. For more information, see:-
Third Exception: File Inputs where most current browsers do not allow the reading of type="file" input elements in a way that is useful.
Use
windowRef.close()
, where windowRef is a window object
reference, such as window, top, parent, self, or a reference
obtained from the window.open() method. You can only close
windows opened by scripts, no others.
Using the DOM the non-standard but widely implemented innerHTML
extension, the following would be sufficient to modify the content
of any element that can have content:
<div id="anID">Some Content</div>
with script of
document.getElementById("anID").innerHTML=
"Some <em>new</em> Content";
Where "anID" is the (unique on the HTML page) ID attribute value
of the element to modify.
The script below adds support for
document.all
capable browsers.
Support for NN4 is also possible, but certain issues mean that
it is not listed here. Using the example above, the call would
be written:
DynWrite('anID',"Some <em>new</em> Content")
With the below code also in the page:
DocDom = (document.getElementById?true:false);
DocAll = (document.all?true:false);
DocStr=''
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 {
DynWrite=new Function("id", "S", "GetRef(id).innerHTML=S; return true")
}
Using Regular Expressions (JavaScript 1.2/JScript 4+) :
String.prototype.lTrim =
function()
{
return this.replace(/^\s+/,'');
}
String.prototype.lTrim =
function()
{
return this.replace(/\s+$/,'');
}
String.prototype.trim =
function()
{
return this.replace(/^\s+|\s+$/g,'');
}
or for all versions (trims characters ASCII<32 not true "whitespace"):
function LTrim(str) {
for (var k=0; k<str.length && str.charAt(k)<=" " ; k++) ;
return str.substring(k,str.length);
}
function RTrim(str) {
for (var j=str.length-1; j>=0 && str.charAt(j)<=" " ; j--) ;
return str.substring(0,j+1);
}
function Trim(str) {
return LTrim(RTrim(str));
}
To reload a page, use location.reload(). However, this depends
upon the cache headers that your server sends. To change this,
you need to alter the server configuration. A quick fix on the
client is to change the page URI so that it contains a unique
element, such as the current time. For example:
location.replace(location.href+'?d='+new Date().valueOf())
If the location.href already contains a Query String, use:
location.replace(location.href+'&d='+new Date().valueOf())
Use the server-side language to generate the javascript:
var jsvar="<%= aspvar %>"; var jsvar="<?php echo $phpvar ?>";
In the normal browser security model, it is impossible for a script from one domain to access the properties of pages served from another domain, or a different protocol. Any attempt to access a property in such cases will result in a "Permission Denied" error. Signed scripts or trusted ActiveX objects can overcome this in limited situations.
There is no built-in way to pause execution in javascript such
as a sleep function, but hosts usually provide a method of some
form. Web browsers are designed for event driven programming and
only provide the
setTimeout
and
setInterval
functions
to facilitate timed delays. The delay before calling Snork will
generally exceed the second parameter to
setTimeout
and
setInterval
due to implementation differences among browsers.
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()
Achieving delays through running a loop of some sort for a pre-defined period is a bad strategy, as that will tend to put CPU use up to 100% and inhibit whatever was supposed to be happening during the delay.
Other (less event driven) hosts have different wait functions,
such as
WScript.Sleep()
in the Windows Script Host.
Javascript variables are loosely typed: the conversion between a
string and a number happens automatically. Since plus (+) is also
used as in string concatenation,
'1' + 1
is equal to
'11'
for its contents. This is a safe-cache copy of the original web site.