comp.lang.javascript FAQ - META 2008-11-19
FAQ server
1 Meta-FAQ meta-questions
You are reading the _comp.lang.javascript_ meta-FAQ,
version 10. It is available on the web at
<URL: http://www.jibbering.com/faq/index.html > in HTML form.
This FAQ provides URLs to further information about ECMAScript
(loosely called 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.
Each day, one section of the FAQ is posted for review and questions,
and as 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:-
<URL: http://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.
2 Javascript Tips
2.1 _Which newsgroups deal with javascript_?
The official Big 8 Usenet newsgroup dealing with javascript is
news:comp.lang.javascript.
Some "language" hierarchies also have *.comp.lang.javascript groups.
CLJ is an unmoderated newsgroup.
2.2 _What questions are on-topic for CLJ_?
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:
news:microsoft.public.scripting.jscript
The comp.lang.javascript newsgroup charter is included in
<URL: http://www.jibbering.com/faq/faq_notes/cljs_charter.html >
2.3 _What should I do before posting to CLJ_?
Before posting to CLJ, you should read this document.
You should also check the Resources section <URL: http://jibbering.com/faq/#onlineResources >
and the Quick Answers section and FYI28/RFC1855 <URL: http://www.rfc-editor.org/fyi/fyi28.txt >.
Search the Web, in particular the CLJ archives at
<URL: http://groups.google.com/group/comp.lang.javascript/topics >.
*How to Ask a Question*
* Read all appropriate posts to the CLJ newsgroup
for several days.
* State your question clearly and concisely.
* Use the Subject: of your post to indicate the type of problem
you have, but include the question in the body as well.
* For a more detailed explanation of formatting, see
"Posting Questions and Replies to comp.lang.javascript" <URL: http://www.jibbering.com/faq/faq_notes/clj_posts.html >.
*Replying*
* Quote only relevant parts of earlier messages, and add your
comments below each quoted section
(FYI28/RFC1855 <URL: http://www.ietf.org/rfc/rfc1855.txt >).
Do not top-post.
* Cite any part of the FAQ that applies.
Be specific and link to the relevant section.
* Avoid being unnecessarily rude, but do not complain about other rude posts.
* Don't quote signatures.
*Posting Code*
* Try to reduce the problem as much as possible.
* Validate the HTML <URL: http://validator.w3.org/ >
* Make sure your code is executable as transmitted.
* Use line breaks, wrap code at 72 characters, and indent in
units of 2-3 spaces (not tabs) to show structure.
* If the script you are including is over 300 lines, please do
not post the full script and just provide a link.
* Mention which platforms and browsers are used or are giving
problems.
* See also the FAQ section on debugging <URL: http://jibbering.com/faq/#debugging >.
* Post in plain-text only. Do not encode it. Do not attach files.
* Do not multi-post; cross-post if necessary.
*What Not to Post*
* Do not post job postings. Job postings should go to
an appropriate regional jobs group.
* Do not post copyright material without permission
from the copyright holder.
Announcements of products relevant to javascript are welcome, but not
more often than once per major release, and then post a short
link to the product's webpage.
2.4 _Why was my post not answered_?
This could be for several reasons:
It was a variation of a frequently asked question and was
therefore ignored by everyone.
Nobody knows the answer.
The person with the answer has not seen the post.
It might not be possible to do what you want to do but perhaps
readers of CLJ are reluctant to answer your post in the negative
when they are not convinced that it cannot be done.
The question was not asked clearly enough, or did not included
enough information to be answered.
The questioner did not realise the need to read the group, for a
few days, to see the answers posted there.
You ignored the
If it is not one of these, then after a few days consider
reposting after checking <URL: http://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.
2.5 _What is ECMAScript_?
ECMAScript is the international standard for JavaScript. JScript
3.0 and JavaScript 1.5 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.
<URL: http://www.ecma-international.org/publications/standards/Ecma-262.htm >
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).
2.6 _What is JScript_?
JScript is Microsoft's implementation of ECMAScript.
Questions that are specific to Microsoft's JScript may also
be appropriately asked at:
news:microsoft.public.scripting.jscript
2.7 _What are object models_?
Object models (OMs) are not part of the ECMAScript 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 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 documents.
2.8 _What is the document object model_?
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 an
ECMAScript 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 different browsers.
<URL: http://jibbering.com/faq/#onlineResources >
<URL: http://www.w3.org/DOM/faq.html >
<URL: http://www.w3.org/DOM/ >
2.9 _Internationalisation and Multinationalisation in javascript.
Internationalisation means using one form which is everywhere both
acceptable and understood. Any international standard not supported by
default can be coded for.
For example, there is an International Standard for numeric Gregorian
date format; but none for decimal and thousands separators.
Multinationalisation means using different forms for different
readers. It cannot work well in general, because it requires a
knowledge of all 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 ECMAScript.
2.10 _I have a question that is not answered in here or
in any of the resources mentioned here but I'm sure it has been
answered in CLJ. Where are the CLJ archives located_?
<URL: http://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.
2.11 _What does the future hold for ECMAScript_?
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:
<URL: http://www.ecmascript.org/ >,
or from news:microsoft.public.dotnet.languages.jscript
3 Javascript Resources
3.1 _What books cover javascript_?
Although many books have been reviewed, most are quite bad and cannot be recommended.
The following list of books been approved by CLJ regulars after
technical review.
_"JavaScript: The Definitive Guide,"_ 5th Edition, By David Flanagan.
ISBN: 0-596-10199-6
<URL: http://oreilly.com/catalog/9780596101992/toc.html >
<URL: http://www.oreilly.com/catalog/jscript5/errata/ >
_"JavaScript Pocket Reference,"_, By David Flanagan.
ISBN-10: 1565925211, ISBN-13: 978-1565925212
<URL: http://oreilly.com/catalog/9780596004118/toc.html >
<URL: http://oreilly.com/catalog/9780596004118/errata/ >
3.2 _What online resources are available_?
*ECMAScript*
* The Official ECMAScript Specification
<URL: http://www.ecma-international.org/publications/standards/Ecma-262.htm >
* ISO/IEC 16262: ISO Standard of ECMA-262 r3 with Corrections
<URL: http://standards.iso.org/ittf/PubliclyAvailableStandards/c033835_ISO_IEC_16262_2002(E).zip >
* ECMAScript on Wikipedia
<URL: http://en.wikipedia.org/wiki/ECMAScript >
*W3C DOM*
* DOM Level 1 ECMAScript Binding
<URL: http://www.w3.org/TR/REC-DOM-Level-1/ecma-script-language-binding.html >
* DOM Level 2 ECMAScript Binding
<URL: http://www.w3.org/TR/DOM-Level-2-HTML/ecma-script-binding.html >
* DOM Level 2 Events
<URL: http://www.w3.org/TR/DOM-Level-2-Events/events.html >
* DOM Level 2 Style
<URL: http://www.w3.org/TR/DOM-Level-2-Style/ >
* DOM Level 3 ECMAScript Binding
<URL: http://www.w3.org/TR/DOM-Level-3-Core/ecma-script-binding.html >
*Browser Documentation*
* Mozilla JavaScript 1.5 reference
<URL: http://developer.mozilla.org/en/docs/JavaScript >
* Online Gecko DOM Reference
<URL: http://developer.mozilla.org/en/docs/Gecko_DOM_Reference >
* Microsoft (D)HTML Reference
<URL: http://msdn2.microsoft.com/en-us/library/ms533050.aspx >
* JScript Reference and Main Microsoft Script Site
<URL: http://msdn2.microsoft.com/en-us/library/hbxc2t98.aspx >
<URL: http://msdn2.microsoft.com/en-us/library/ms950396.aspx >
* Opera Documentation
<URL: http://www.opera.com/docs/specs/#ecmascript >
<URL: http://www.opera.com/docs/specs/js/ >
<URL: http://www.opera.com/docs/specs/js/ecma >
* ICab's Inscript documentation
<URL: http://www.muchsoft.com/inscript/ >
* Safari JavaScriptCore documentation
(nothing)
* Netscape 4 JavaScript (reproduced by Sun Microsystems, Inc.)
<URL: http://docs.sun.com/source/816-6408-10/ >
* Index of Archived Netscape 4 JavaScript docs online and for download
<URL: http://devedge-temp.mozilla.org/library/manuals/2000/javascript/1.3/reference/ >
* Archived documentation for MSIE 3.x
<URL: http://members.tripod.com/%7Ehousten/download/ >
*Javascript Library Groups (Google Groups)*
No javascript libraries are endorsed by this group.
If you are looking for help using a library, visit that library's
discussion group instead.
* jQuery [English]
<URL: http://groups.google.com/group/jquery-en >
* Prototype & Scriptaculous
<URL: http://groups.google.com/group/prototype-scriptaculous >
*Non-Browser javascript Implementations*
* Developing Dashboard Widgets
<URL: http://developer.apple.com/macosx/dashboard.html >
* Win32 Scripting, Using Scripting to Automate Windows
<URL: http://cwashington.netreach.net/ >
* Whitebeam Apache Module - Server Side JavaScript in Apache;
<URL: http://www.whitebeam.org/ >
* Digital Mars DMD Script, console and MS Active Script implementation of ECMAScript,
claimed to be faster than other implementations:
<URL: http://www.digitalmars.com/dscript/ >
* FESI - a free implementation of ECMAScript in Java
<URL: http://www.lugrin.ch/fesi/index.html >
4 Quick Answers: Numbers
4.1 _How do I convert a Number into a String with exactly 2 decimal places_?
4.2 _Why does simple decimal arithmetic give strange results_?
4.3 _Why does K = parseInt('09') set K to 0_?
4.4 _Why does 1+1 equal 11_? or How do I convert a string to a number?
4.5 _How do I generate a random integer from 1 to N_?
5 Quick Answers
5.1 _How do I protect my javascript code_?
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.
Your code is likely protected under copyright laws. See:
<URL: http://www.wipo.int/about-ip/en/copyright.html >
<URL: http://webdesign.about.com/od/copyright/Copyright_Issues_on_the_Web_Intellectual_Property.htm >
5.2 _How can I disable the back button 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.
<URL: http://msdn2.microsoft.com/en-us/library/ms536712.aspx >
<URL: http://docs.sun.com/source/816-6408-10/location.htm#1194240 >
5.3 _How can I access the client-side filesystem_?
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 Google Groups archives <URL: http://groups.google.com/group/comp.lang.javascript/topics >
for previous posts on the subject.
<URL: http://msdn2.microsoft.com/en-us/library/z9ty6h50.aspx >
<URL: http://www.javaworld.com/javaworld/jw-10-1998/jw-10-apptowin32.html >
5.4 _How can I see in javascript if a web browser accepts cookies_?
Write a cookie and read it back and check if it's the same.
<URL: http://www.w3schools.com/js/js_cookies.asp >
Additional Notes:
<URL: http://www.jibbering.com/faq/faq_notes/cookies.html >
<URL: http://www.ietf.org/rfc/rfc2965.txt >
<URL: http://www.galasoft-lb.ch/myjavascript/consulting/2001012701/ >
<URL: http://www.cookiecentral.com/ >
5.5 _How can I prevent access to a web page by using javascript_?
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.
5.6 _How do I communicate between frames in a web browser_?
To reference another frame, you simply need to step through the
frame hierarchy: parent is the page the frame is
definedin, 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().
Note that it is not possible to communicate between frames on
different domains this way.
5.7 _How do I find the size of the window_?
Here is a detailed explanation of a cross-browser strategy to
find the dimensions of the viewport, excepting all chrome
(excludes scrollbars, et c).
We can consider various properties:
window.innerWidth
document.clientWidth
document.documentElement.clientWidth
document.body.clientWidth
Of the browsers that have an innerWidth property, most
include scrollbar dimensions. Some versions of KHTML browsers
(including Safari 2) do _not_ include scrollbar width.
The window.inner* properties are unreliable and not
useful here. We don't want scrollbar dimensions included.
document.clientWidth
Certain versions of KHTML, including Safari 2, have
document.clientHeight and document.clientWidth
properties. Where supported, these rare properties accurately
return the height and width of the viewport, without including
scrollbar dimensions.
document.documentElement.clientWidth
document.body.clientWidth
MSHTML (Trident), Firefox (Gecko), Opera (Presto), and Safari
(Webkit) all support clientHeight on document.body
and document.documentElement. The difficulty is figuring out
which one is reliable. In other words which object to get the
clientHeight property from:documentElement or body?
What the number returned from either of these properties
represents depends on the environment. The environment includes
the browser, its version, and the rendering mode of the document.
In quirks mode, we'll mostly want to use body.clientHeight
(except for in Safari 2).
document.body.clientHeight
Some environments will return the viewport height. Others will
return 0. Yet others will return the clientHeight of
the BODY element.
document.documentElement.clientHeight
This is the more "standard" property for getting the height of
the viewport. It usually "works" in modern browsers in
standards mode. Notable exceptions include Safari 2 and
Opera <= 9.25, both of which return the clientHeight
of the html_element_. (Oddly, Opera <= 9.25
in standards mode returns the width of the viewport for
documentElement.clientWidth).
With the exception of Safari 2, body.clientHeight is reliable
where documentElement.clientHeight is found to be unreliable.
For example, in Safari 3+, Opera, and Mozilla, all in quirks mode,
document.documentElement.clientHeight returns the clientHeight
of the html element (this may seem unsurprising but
it is not what we want).
Conversely, document.body.clientHeight will return
the height of the viewport in most cases where
document.documentElement.clientHeight does not. An exception
to that is Safari 2, where documentElement.clientHeight
and body.clientHeight both return the height of their
corresponding element (not what we want).
By using a combination of Feature Testing and Capability Testing,
the dimensions of the viewport can be strategically retrieved
from the property that works in the environment the script is
running in. The trick is determining which property willgive us
the value we want.
Since document.clientHeight is reliable where
(rarely) supported, and since browsers that support this property
don't return the viewport dimensions from
document.body.clientHeight or
document.documentElement.clientHeight, this should be the
very first condition:
// Safari 2 uses document.clientWidth (default).
if(typeof document.clientWidth == "number") {
// use document.clientWidth.
}
The next strategy is to determine if
document.documentElement.clientHeight property is unreliable.
It is deemed "unreliable" when it is either 0 or taller
than the viewport.
Determining if documentElement.clientHeight is 0 is easy.
The result is stored in a variable IS_BODY_ACTING_ROOT.
var docEl = document.documentElement,
IS_BODY_ACTING_ROOT = docEl && docEl.clientHeight === 0;
docEl = null;
To determine if documentElement.clientHeight returns
a value taller than the viewport, we need a Capability Test.
If we can force documentElement to be very tall
(taller than a normal viewport) we can then check to see if
documentElement.clientHeight returns that "very tall" number.
If it does, then it is unreliable.
We can force documentElement to be taller than the viewport
(or any "normal" viewport) by adding a div to the body,
give that div a height larger than any normal monitor,
and then check to see if documentElement.clientHeight is
that high (or "almost" that high, to account for documentElement
having a border).
// Used to feature test Opera returning wrong values
// for documentElement.clientHeight.
// The results of this function should be cached,
// so it does not need to be called more than once.
function isDocumentElementHeightOff(){
var d = document,
div = d.createElement('div');
div.style.height = "2500px";
d.body.insertBefore(div, d.body.firstChild);
var r = d.documentElement.clientHeight &> 2400;
d.body.removeChild(div);
return r;
}
We can use this function to see if we should use
body.clientHeight, instead. (but only after checking if
document.clientHeight is supported).
// Safari 2 uses document.clientWidth (default).
if(typeof document.clientWidth == "number") {
// use document.clientHeight/Width.
}
else if(IS_BODY_ACTING_ROOT || isDocumentElementHeightOff()) {
// use document.body.clientHeight/Width.
} else {
// use document.documentElement.clientHeight/Width.
}
The preceding strategy was developed by Garrett Smith with input
from John David Dalton. A complete and tested example can be found
in APE Library under APE.dom.getViewportDimensions.
Source code:
<URL: http://dhtmlkitchen.com/ape/build/dom/viewport-f.js >.
APE is publicly released under Academic Free License.
APE home: <URL: http://dhtmlkitchen.com/ape/ >.
Note: The dimensions cannot be determined accurately until after
the document has finished loading.
<URL: http://msdn2.microsoft.com/en-us/library/ms533566.aspx >
<URL: http://developer.mozilla.org/en/DOM/window.innerWidth >
<URL: http://dev.opera.com/articles/view/using-capability-detection/ >
5.8 _How do I check to see if a child window is open, before opening another_?
var myWin;
function openWin(aURL) {
if (!myWin || myWin.closed ) {
myWin = window.open(aURL,'myWin');
} else {
myWin.location = aURL;
myWin.focus();
}
}
<URL: http://msdn2.microsoft.com/en-us/library/ms533574.aspx >
<URL: http://docs.sun.com/source/816-6408-10/window.htm#1201877 >
5.9 _Why does framename.print() not print the correct frame in IE_?
IE prints the frame that has focus when you call the print
method frameref.focus();frameref.print();
<URL: http://msdn2.microsoft.com/en-us/library/ms976105.aspx >
5.10 _How do I get the value of a form control_?
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;
value = +contrl.value; //string to number: see 4.2
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:-
<URL: http://www.jibbering.com/faq/faq_notes/form_access.html >
Third Exception: File inputs. Most current browsers do not allow
reading of type="file" input elements in a way that is useful.
5.11 _How do I close a window and why does it not work on the first one_?
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.
<URL: http://msdn2.microsoft.com/en-us/library/ms536367.aspx >
<URL: http://docs.sun.com/source/816-6408-10/window.htm#1201822 >
<URL: http://developer.mozilla.org/en/docs/DOM:window.open#FAQ >
5.12 _How do I modify the content of the current page_?
Using the non-standard but widely implemented innerHTML property:
<div id="anID">Some Content</div> with script:
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.
If the new content is only text and does not need to replace existing HTML,
it is more efficient to modify the data property of a text node.
document.getElementById("anID").firstChild.data = "Some new Text";
Note: Make sure the element exists on the page (and has been parsed) before trying to
reference it.
<URL: http://www.w3.org/TR/DOM-Level-2-Core/core.html#ID-FF21A306 >
<URL: http://msdn.microsoft.com/en-us/library/cc304097(VS.85).aspx >
<URL: http://msdn2.microsoft.com/en-us/library/ms533897.aspx >
<URL: http://developer.mozilla.org/en/Whitespace_in_the_DOM >
<URL: http://developer.mozilla.org/en/docs/DOM:element.innerHTML >
<URL: http://www.jibbering.com/faq/faq_notes/alt_dynwrite.html >
5.13 _How do I trim whitespace_?
Use a regular expression:
function trimString(s) {
return s.replace(/^\s+|\s+$/g,'');
}
<URL: http://docs.sun.com/source/816-6408-10/regexp.htm >
<URL: http://msdn2.microsoft.com/en-us/library/6wzad2b2.aspx >
<URL: http://en.wikipedia.org/wiki/Regular_expression >
<URL: http://www.merlyn.demon.co.uk/js-valid.htm >
5.14 _How do I force a reload from the server/prevent caching_?
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())
<URL: http://www.mnot.net/cache_docs/ >
<URL: http://docs.sun.com/source/816-6408-10/date.htm >
5.15 _How do I get a perl/asp/php variable into client-side javascript_?
Use the server-side language to generate the javascript:
var jsvar = "<%= aspvar %>";
var jsvar = "<?php echo $phpvar ?>";
5.16 _Why do I get permission denied when accessing a frame/window_?
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.
<URL: http://msdn2.microsoft.com/en-us/library/ms533028.aspx >
5.17 _How do I make a 10 second delay_?
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 may
exceed the second parameter to setTimeout and setInterval
due to implementation differences among browsers.
To call the function Snork(), approximately 10 seconds
after the function Moomin() completes, 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 inhibit whatever was supposed to
be happening during the delay, including blocking user interation.
Other (less event driven) hosts have different wait functions,
such as WScript.Sleep() in the Windows Script Host.
<URL: http://msdn2.microsoft.com/en-us/library/ms536753.aspx >
<URL: http://docs.sun.com/source/816-6408-10/window.htm#1203758 >
<URL: http://en.wikipedia.org/wiki/Event-driven_programming >
<URL: http://jibbering.com/faq/faq_notes/misc.html#mtSetTI >
5.18 _How do I change print settings with window.print()_?
In a normal security environment, 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, Netscape, and Opera.
<URL: http://www.meadroid.com/scriptx/ >
<URL: http://msdn2.microsoft.com/en-us/library/ms976105.aspx >
5.19 _I have <a href="javascript:somefunction()"> what ... _?
Whatever the rest of your question, this is generally a very bad idea.
The javascript: pseudo protocol was designed to replace the
current document with the value that is returned from the expression.
For example:
<a href="javascript:'<h1>' + document.lastModified + '</h1>'">lastModified</a>
will result in replacing the current document with the value
returned from document.lastModified, wrapped in an <h1>
tag.
When the expression used evaluates to an undefined value
(as some function calls do), the contents of the current page are not
replaced. Regardless, some browsers (notably IE6) interpret this as
navigation and will enter into a 'navigation' state where GIF
animations will stop working.
It is also possible for IE to be configured such that it supports
javascript but not the javascript: protocol. This results
in the user seeing a protocol error for javascript: URIs.
The javascript: pseudo protocol creates accessibility and
usability problems in user agents that do not support javascript, or
have javascript disabled. It provides no fallback for when the script
is not supported.
Instead, use
<a href="something.html" onclick="somefunction();return false">
where something.html is a meaningful alternative. Alternatively,
attach the click callback using an event registry.
<URL: http://www.useit.com/alertbox/20021223.html >
5.20 _My element is named myselect[], how do I access it_?
Form controls with any "illegal" characters can be accessed with
formref.elements["myselect[]"] - The bracket characters,
amongst others, are illegal in ID attributes and javascript
identifiers, so you should try to avoid them as browsers may
handle them incorrectly.
<URL: http://msdn2.microsoft.com/en-us/library/ms537449.aspx >
<URL: http://docs.sun.com/source/816-6408-10/form.htm >
<URL: http://www.jibbering.com/faq/faq_notes/faq_notes.html#FAQN4_25 >
5.21 _How do I detect Opera/Netscape/IE_?
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, but which one you
choose depends on why you want to redirect browsers. If it's to
offer different CSS stylesheets, then <URL: http://w3development.de/css/hide_css_from_browsers/ >
shows many techniques. For Scripting, _object_ detection
is a better method to use.
<URL: http://www.quirksmode.org/js/support.html >
It is also known as feature detection.
Object/feature 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.
<URL: http://developer.mozilla.org/en/docs/Using_Web_Standards_in_your_Web_Pages:Developing_Cross_Browser/Cross_Platform_Pages >
<URL: http://www.jibbering.com/faq/faq_notes/not_browser_detect.html >
<URL: http://dev.opera.com/articles/view/using-capability-detection/ >
<URL: http://developer.apple.com/internet/webcontent/objectdetection.html >
5.22 _How do I disable the right mouse button_?
The oncontextmenu is a proprietary method and is not supported on
all browsers.
<body oncontextmenu="return false">
5.23 _How do I change the confirm box to say yes/no or default to cancel_?
The buttons on a confirm box cannot be changed, nor can you
specify a default button. However, you should be able to change
the question so that "OK" is suitable as the default.
e.g. change "We will now buy ourselves a Porsche with your credit
card, Do you want to continue with this transaction _OK_ Cancel"
to "We will now buy ourselves a Porsche with your credit card,
Would you like to abandon this transaction? _OK_ Cancel"
5.24 _How do I log-out a user when they leave my site_?
This cannot be done reliably. Here's why:
The user may disable javascript so the log-out script will
never execute.
The user may not be on-line when they close your web page.
Javascript errors elsewhere in the page may prevent the script
executing.
The browser may not support the onunload event, or may not fire
it under certain circumstances, so the log-out function will
not execute.
The URL below has more information.
<URL: http://groups.google.com/groups?selm=BlmZ7.55691%244x4.7344316%40news2-win.server.ntlworld.com >
5.25 _How do I format the lastModified date with javascript_?
Apparently, new Date() reads document.lastModified
correctly, though problems
can occur if the browser returns only two digits for the year.
In particular, time offset, field order and separators may vary.
It is also reliant on the server's clock having been correctly
set at the time of upload. See the URL
below.
<URL: http://www.merlyn.demon.co.uk/js-date2.htm#lM >
5.26 _Why are my rollovers so slow_?
Images are cached by the browser depending on the headers sent by
the server. If the server does not send sufficient information
for the browser to decide the image is cacheable, the browser
will check if the image has been updated every time you change the
src of an image (in some user settings). To overcome this you
must send suitable headers.
<URL: http://www.mnot.net/cache_docs/ >
5.27 _How do I change the text in the url/location bar_?
This text can only be altered by changing the URL of the page.
5.28 _How do I prompt a "Save As" dialog for an accepted mime type_?
It is not possible with client-side javascript.
Some browsers accept the Content-Disposition header, but this
must be added by the server. Taking the form:-
Content-Disposition: attachment; filename=filename.ext
<URL: http://classicasp.aspfaq.com/general/how-do-i-prompt-a-save-as-dialog-for-an-accepted-mime-type.html >
<URL: http://support.microsoft.com/kb/q260519/ >
5.29 _How do I run a server side script_?
You trigger a server-side script by sending an HTTP request.
This can be acheived by setting the src of an img,
Image, frame, or iframe,
or by using XHR.
An image will also
"swallow" the data sent back by the server, so that they will
not be visible anywhere.
var dummyImage = new Image();
dummyImage.src = "scriptURL.asp?param=" + varName;
Mozilla, Opera 7.6+, Safari 1.2+, and Windows IE 7
provide the XMLHttpRequest object
(Windows IE versions 5+, provides ActiveX to acheive an analagous
effect). XMLHttpRequest can send HTTP requests to
the server, and provides access the responseText or responseXML
(when the response is XML), and HTTP header information.
<URL: http://jibbering.com/2002/4/httprequest.html >
<URL: http://www.w3.org/TR/XMLHttpRequest/ >
<URL: http://developer.mozilla.org/en/XMLHttpRequest >
<URL: http://msdn.microsoft.com/en-us/library/ms537505(VS.85).aspx >
5.30 _I have window.status="Moomin"; why doesn't the statusbar change_?
When changing the status in an event (e.g. onmouseover) you
should return true from the event. Also a number of browsers
require a short delay before setting the status to overcome their
default behaviour with the statusbar.
onevent="setTimeout('window.status=\'Moomin\'',15);"
Most browsers are configured, by default, to disallow scripts from setting
the status bar text.
5.31 _How do I modify the current browser window_?
In a default security environment you are very limited in how much
you can modify the current browser window. You can use
window.resizeTo or window.moveTo to resize or move a
window respectively, but that is it. Normally you can only
suggest chrome changes in a window.open.
<URL: http://msdn2.microsoft.com/en-us/library/ms536651.aspx >
<URL: http://developer.mozilla.org/en/docs/DOM:window.open >
5.32 _How do I POST a form to a new window_?
Use the target attribute on the form, opening a window with
that name and your feature string in the onsubmit handler of the
FORM.
<form action="..." target="wndname" onsubmit="window.open('',this.target,'features');return true;">
<URL: http://www.htmlhelp.com/reference/html40/forms/form.html >
5.33 _How do I download a page to a variable_?
Within a web-page use the XMLHttpRequest object, see:
<URL: http://jibbering.com/2002/4/httprequest.html >
<URL: http://www.ajaxtoolbox.com/ >
5.34 _How do I access a property of an object using a string_?
There are two ways to access properties: the dot notation and
the square bracket notation. What you are looking for is the square
bracket notation in which the dot, and the identifier to its right,
are replaced with a set of square brackets containing a string. The
value of the string matches the identifier. For example:-
//dot notation
var bodyElement = document.body;
//square bracket notation, using an expression
var bodyElement = document["bo"+"dy"];
<URL: http://www.jibbering.com/faq/faq_notes/square_brackets.html >
5.35 _When should I use eval_?
The eval() function should _only_ be used when it is necessary to
evaluate a string supplied or composed at run-time; the string
can be anything from a simple (but unpredictable) expression such
as "12 * 2.54" to a substantial piece of javascript code.
<URL: http://www.jibbering.com/faq/#propertyAccessAgain >
<URL: http://www.jibbering.com/faq/faq_notes/square_brackets.html >
5.36 _Why doesn't the global variable "divId" always refer to the element with id="divId"_?
Microsoft introduced a shortcut that can be used to reference
elements which include an id attribute where the
id becomes a globally-accessible property. Some browsers reproduce
this behavior. Some, most notably Gecko-based browsers (Netscape and Mozilla),
do so only in "quirks" mode. The best approach is the document.getElementById
method, which is part of the W3C DOM standard and implemented
in modern browsers (including IE from version 5.0). So an
element with id="foo" can be referenced
with:-
var el = document.getElementById("foo");
Note: make sure not to use the same id twice in the same document
and do not give an element a name that matches an id
of another in the same document or it will trigger bugs in MSIE <= 7 with
document.getElementsByName and document.getElementById.
<URL: http://developer.mozilla.org/en/docs/Using_Web_Standards_in_your_Web_Pages:Using_the_W3C_DOM#Accessing_Elements_with_the_W3C_DOM >
<URL: http://www.jibbering.com/faq/faq_notes/faq_notes.html#FAQN4_41 >
5.37 _How do I open a new window with javascript_?
New windows can be opened on browsers that support the
window.open function and are not subject to the action of any
pop-up blocking mechanism with code such as:-
var wRef;
if(window.open){
wRef = window.open("http://example.com/page.html","windowName");
}
<URL: http://developer.mozilla.org/en/docs/DOM:window.open >
<URL: http://www.infimum.dk/HTML/JSwindows.html >
5.38 _How do I get my browser to report javascript errors_?
* Windows IE
Wait until a little yellow
triangle appears at the left end of the status bar, double click
on it and, when the error dialog box appears, check the "Always
show errors" checkbox it contains.
Or, Internet Options, Advanced, deselect "Disable Script Debugging",
select "Display a notification ...".
* Firefox
<URL: http://www.getfirebug.com/ >.
* Opera
Tools > Advanced > Error console
<URL: http://dev.opera.com/articles/view/introduction-to-opera-dragonfly/ >
* Safari
To display the Develop menu in Safari 3.1 or higher, select
the checkbox labeled "Show Develop menu in menu bar" in
Safari's Advanced Preferences panel.
<URL: http://developer.apple.com/internet/safari/faq.html#anchor14 >
* Chrome
JavaScript Console: click the Page menu icon and select
Developer > JavaScript Console. From here, you'll be
able to view errors in the JavaScript execution, and enter
additional javascript commands to execute.
JavaScript Debugger: available as Page menu icon > Developer
> Debug JavaScript, the debugger provides a command prompt from which you
can set breakpoints, backtrace, and more. Type help at the debugger
command line to get started.
<URL: http://www.google.com/chrome/intl/en/webmasters-faq.html#jsexec >
* Mac IE
Use the Preferences dialog.
5.39 _What is Ajax_?
Ajax
is shorthand for Asynchronous JavaScript And XML. The technology is
based on the XMLHttpRequest Object.
At its simplest, it is the sending/retrieving of new data from the server
without changing URL's or reloading the current page.
Mozilla Documentation:
<URL: http://developer.mozilla.org/en/docs/XMLHttpRequest >
MSDN Documention:
<URL: http://msdn2.microsoft.com/en-us/library/ms535874.aspx >
<URL: http://msdn2.microsoft.com/en-us/library/ms759148.aspx >
Libraries and Tutorial Sites:
<URL: http://jibbering.com/2002/4/httprequest.html >
<URL: http://www.ajaxtoolbox.com/ >
An alternative to the XMLHttpRequest Object is Remote Scripting:
<URL: http://www.ashleyit.com/rs/main.htm >
5.40 _Why is my Ajax page not updated properly when using an HTTP GET request in Internet Explorer_?
Microsoft Internet Explorer caches the results of HTTP GET requests. To ensure that the
document is retrieved from the server, you will need to use the POST Method.
<URL: http://msdn2.microsoft.com/en-us/library/ms536648.aspx >
6 Comments and Suggestions
6.1 _Why do some posts have <FAQENTRY> in them_?
If a poster feels that the question they are answering should be
covered in the FAQ, placing <FAQENTRY> in the post lets the FAQ
robot collect the messages for easy review and inclusion. A Draft Proposal
for the FAQ is requested and appreciated.
The <FAQENTRY> should not be used in posts except in
conjunction with a suggestion/proposal for the FAQ. It should
also not be literally quoted in replies, instead it should be
partly obscured as, e.g. <FAQ**TRY> or similar.
6.2 _How do I make a suggestion_?
To make a suggestion to the FAQ, use either the FAQENTRY method
above, or email Garrett Smith dhtmlkitchen@gmail.com (current FAQ editor)
or Jim Ley (jim.ley@gmail.com). All comments, suggestions, and
especially corrections are welcome.
1_Meta-FAQ meta-questions_
2_Javascript Tips_
2.1 *Which newsgroups deal with javascript?*
2.2 *What questions are on-topic for CLJ?*
2.3 *What should I do before posting to CLJ?*
2.4 *Why was my post not answered?*
2.5 *What is ECMAScript?*
2.6 *What is JScript?*
2.7 *What are object models?*
2.8 *What is the document object model?*
2.9 *Internationalisation and Multinationalisation in javascript.*
2.10 *I have a question that is not answered in here or
in any of the resources mentioned here but I'm sure it has been
answered in CLJ. Where are the CLJ archives located?*
2.11 *What does the future hold for ECMAScript?*
3_Javascript Resources_
3.1 *What books cover javascript?*
3.2 *What online resources are available?*
4_Quick Answers: Numbers_
see <URL: http://jibbering.com/faq/#FAQ4 >
Or Wednesdays FAQ posting.
5_Quick Answers_
5.1 *How do I protect my javascript code?*
5.2 *How can I disable the back button in a web browser?*
5.3 *How can I access the client-side filesystem?*
5.4 *How can I see in javascript if a web browser accepts cookies?*
5.5 *How can I prevent access to a web page by using javascript?*
5.6 *How do I communicate between frames in a web browser?*
5.7 *How do I find the size of the window?*
5.8 *How do I check to see if a child window is open, before opening another?*
5.9 *Why does framename.print() not print the correct frame in IE?*
5.10 *How do I get the value of a form control?*
5.11 *How do I close a window and why does it not work on the first one?*
5.12 *How do I modify the content of the current page?*
5.13 *How do I trim whitespace?*
5.14 *How do I force a reload from the server/prevent caching?*
5.15 *How do I get a perl/asp/php variable into client-side javascript?*
5.16 *Why do I get permission denied when accessing a frame/window?*
5.17 *How do I make a 10 second delay?*
5.18 *How do I change print settings with window.print()?*
5.19 *I have <a href="javascript:somefunction()"> what ... ?*
5.20 *My element is named myselect[], how do I access it?*
5.21 *How do I detect Opera/Netscape/IE?*
5.22 *How do I disable the right mouse button?*
5.23 *How do I change the confirm box to say yes/no or default to cancel?*
5.24 *How do I log-out a user when they leave my site?*
5.25 *How do I format the lastModified date with javascript?*
5.26 *Why are my rollovers so slow?*
5.27 *How do I change the text in the url/location bar?*
5.28 *How do I prompt a "Save As" dialog for an accepted mime type?*
5.29 *How do I run a server side script?*
5.30 *I have window.status="Moomin"; why doesn't the statusbar change?*
5.31 *How do I modify the current browser window?*
5.32 *How do I POST a form to a new window?*
5.33 *How do I download a page to a variable?*
5.34 *How do I access a property of an object using a string?*
5.35 *When should I use eval?*
5.36 *Why doesn't the global variable "divId" always refer to the element with id="divId"?*
5.37 *How do I open a new window with javascript?*
5.38 *How do I get my browser to report javascript errors?*
5.39 *What is Ajax?*
5.40 *Why is my Ajax page not updated properly when using an HTTP GET request in Internet Explorer?*
6_Comments and Suggestions_
6.1 *Why do some posts have <FAQENTRY> in them?*
6.2 *How do I make a suggestion?*