JavaScript Triggers

by Peter-Paul Koch

140 Reader Comments

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  1. To me it seems that you follow standards by their letters, not by their intention. The future-compatibility is one of the things that drive XHTML forward.
    Why should I bother about adding a sniffer later when I can avoid the problems now? Perhaps I have something else to do when my customers of the old days come and complain?
    Of course XML is extensible, that is no problem, but the mechanism for extension is XML-NS not a copy-paste-dtd.
    Browsers are made to understand and interpret (X)HTML and not any XML that you throw at them (though some do so).
    A custom DTD or XSD might be appropriate in an intranet environment, of course. But in the web, I try to keep things simple and not to do simple tricks now that lead to problems later.

    Let me be a bit extreme now.
    In fact, the method we talk about is a hack: Todays Browsers do not require/check for XHTML, so we give them what we like.

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  2. Please excuse my use of capital letters for non-names. My German tongue tricked me again.

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  3. Doesn’t the BitfluxCMS ( do something like this (correct me if I’m wrong). It uses XML and XSLT as a template engine. This means you could theoretically do something like <tag required=“yes”> and then let the server-side XSLT parse it.

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  4. It’s not likely that you’re going to spend any significant time building a sniffer mostly because anyone using JS already has one built in or has pulled one from another site and secondly because they are so extremely simple to do. That’s not going to take any time away from more important aspects of a project. And if you were worried about one of your element/attributes being a problem in the future you’d probably already get a plan in place prior to customers complaining.

    An intranet IS the best place for custom solutions like this, but it’s not the only place. It’s up to the developer to determine what the needs of the consumer are and whether the benefits outway any potential risks.

    As far as I know all the major browsers today have support for XML. The current use of XHTML allows for backward compatability and forward extensibility. This means that we can send it as XML/XHTML to apps that understand it and HTML to apps that don’t. Either way it would still be valid per the recommendations. One might say that that is a hack but the way I read it it’s by design.

    It’s the difference betwee “should” and “must”. “Must” is an absolute – you CANNOT do it any other way. While “should” is not absolute – you CAN do it another way but here’s the way we recommend. Too many people read “should” as “must”.

    Yes there are multiple methods for defining document elements, families of elements, and extension modules. DTD, Namespaces, Schema or XSD. In many cases they can be complimentary (i.e. see XHTML modularization). I’m unsure what you mean about a “cut and paste” DTD. DTD’s are just a very simple way to define the document to the user agent. It came out before namespaces and XSD so it’s likely to be understood by a wider variety of industry tools and it’s easily discarded when no longer in use.

    Everyone acts as though this is high maintenance work. If I have 120 XHTML documents sitting on a server and decide to no longer use the DTD or use some attribute does anyone really think I’m going to go into 120 documents and manually strip out each and every occurance. No I’m going to at the very least allow my IDE’s find/replace or regex engine do it for me, create an XSLT file for transforming the docs, or strip a couple of lines out of my JSP/PHP code. We’re talking a few minutes worth of effort if you’ve coded thing right from the beginning. Better yet I’m going to have it already coded so that it can be turned on or off from a property file or from a flag from the user agent.

    I think all the arguments so far against the technique are trying to make it sound much more complex and much more fragile than it really is. The truth is that the approach while being “experimental” is already in use by plenty of people and doesn’t in any way go against the existing standards or even run affoul of any best practices tips I’ve seen to date.

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  5. “What is the point of writing to standards if you are just inventing your own?”

    XML : eXtensible Markup Language
    XHTML : eXtensible Hypertext Markup Language

    Extensibility is part of the standard, Jacob.

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  6. The XHTML 1.0 Recommendation (the standard) says under “A.1.” (a normative appendix):
    “The W3C recommends that you use the authoritative versions of these DTDs at their defined SYSTEM identifiers when validating content.”

    True: XML is about extensibility. Yet the intended mechanism for this is “XML Namespaces” which plays unfortunately not well with DTDs (that in turn root in SGML and thus do not yet adhere to our nice extensibility philosophy). One would have to use the XSD
    schemes for validation and use namespaces for custom attributes.
    If you just replace the doctype you do not extend XHTML but instead replace it with your own vocabulary. No fancy “valid XHTML button” then, and rightfully so. This is Jacobs point, I guess.

    To Michael Havard: Of course, in most of the cases anyone uses the custom DTD-technique everything will probably go fine.
    But if you have all the changes already prepared that are necessary in case your approach should break in future – why not just apply them now and save the double work?
    And honestly – do you already know what exactly these workarounds will be? I am not talking about just some object sniffer, but about the case where future standards introduce your syntax with a different meaning or using different attribute values (which is more probable). Turning off your behaviors to new agents will not suffice, because the behavior of your page is going to differ among user agents.

    I see my opinions might be a bit standards-zealous, but hey: This site is a member of “The Web Standards Project” after all.
    Of course, on the bottom line I also agree that this method has been marked as being “experimental and controversial”. So anyone who reads the article has been warned, hopefully will consider such dangers, and make the best out of this creative approach.

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  7. You can use this code to make sure the user doesn’t paste info to get them over the maxlength of the textarea:

    First add the following to the textarea wher the onkeypress event is added:
    x.onpaste = checkLength;

    Then add this to the checkLength function:
    this.value = this.value.substring(0, max);

    You may also want to check the conditional logic to read as it makes sure the max is the true max sent and not one less:
    if(this.value.length >= max){

    Just thought I would share what I changed when using the script, thanks for the article!

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  8. I have been using custom DTDs the way described in the article for quite some time – even going as far as putting rollover states for images in the HTML like this (not everybody’s cup of tea):

      <state label=“focus” src=“pix/focus.gif” >
      <state label=“on” src=“pix/on.gif” >

    For completeness, I would add that many people (mostly backend programmers) consider custom DTDs unacceptable, because they make a website too “top-heavy”, as it adds another 30/50k to the first page a user visits.

    A solution I used in that case is to add a “preparatory” script at the beginning of each page, roughly in this form:

    window.onload = function()
      document.getElementById( ‘x’ ).addAttribute( ‘aname’, ‘avalue’ );
      document.getElementById( ‘y’ ).addAttribute( ‘bname’, ‘bvalue’ );
      //… etc

    Again, this approach may or may not be to people’s taste.

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  9. Discussion seems incomplete without including mention of microsoft’s css behaviors extension and .htc files.  Far simpler interface, and a truer form of “trigger”, but admittedly probably not useful for the form validation example in this article.

    Lots of good comments though, to which i would add that if your XHMTL is being passed through an XSLT layer, you can output the validator scripts dynamically, before it ever reaches the client.

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  10. I guess you could say I’m “trigger happy” now!

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  11. Peter Paul Koch is not writing here something interesting that has news value.

    In fact he keeps rewriting his more than one and half year old writing

    Forms, usability, and the W3C DOM : Comments
    By Peter-Paul Koch
    Published on May 30, 2003

    and sells this for newbees as a new article and as seen here very many praise him.
    He just has added doubtful paragraph about custom DTDs and thats pretty much it.

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  12. Matching a class name in JavaScript can be tricky, especially if you want to be able to apply more than one class to an element and still not match trick classes (like on the last list item).
    In this example we’re looking for an expression that matches the first four items in the list.
    Note that the last method is the correct approach, the first two are wrong.

    <li class=“two”>Crocodile</li>
    <li class=“one two”>Beaver</li>
    <li class=“two three”>Pig</li>
    <li class=“one two three”>Monkey</li>
    <li class=“one-two-three”>Horse</li>

    Following two methods will not work.

    if (element.className == “two”) {
    // Matches first list item only

    if (element.className.indexOf(“two”) != -1) {
    // Matches all list items

    This one however will.

    if (element.className.match(/( |^)(two)( |$)/)) {
    // Matches first four list items

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  13. var temp = element.classname.split(” “);

    for(i=0; i<temp.length; i++)
    // now match with == or use switch/case
    // and all is well

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  14. Inspired by PPK’s article, I revised the forms for the Drink-Drive-Lose Ad Challenge:

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  15. Marek Mänd is not writing here something interesting that has news value.

    In fact he has written absolutely nothing that has any value whatsoever.

    And sells this for newbees as a viable critique of an article he couldn’t have written himself.

    He just has established beyond doubt that he’s jealous and thats pretty much it.

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  16. Oops. I fell for the Capital letter meme.

    PPK’s method is just one method. We can rule out behaviours because:
    1. They don’t validate
    2. They are browser proprietary

    Admitted, PPK’s method fails #1 too but it does pass #2. Like it or not I still say that a custom attribute is the most semantically correct way.

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  17. As Adrian and Dave pointed out, the ability to use the class attribute for things other than CSS classes is allowed. I’m not sure I follow the idea that this doesn’t allow us to keep the seperation between structure, presentation and behaviour, as the class attribute is already used to “bind” presentation to a structural element, why is this very same technique frowned upon for behaviour?

    Would Peter-Paul feel that having an attribute labelled “behaviour” with the ability to specificy function/object names better suited? Because this is essentially what the classnames are doing, only for presentation.

    The argument that mixing behaviour in with class names doesn’t allow for a clean seperation between structure and behaviour doesn’t really hold water with me, as this is exactly the same technique that is used to associate presentation with structure.

    However, I DO see a need to maybe seperate behaviour assignments from presentation assignments: this will lead to confusion (although were quite fortunate that this wont lead to a problem similar to what namespaces hope to clear up, as a classname could contain a behaviour called “button” and a CSS class called “button”)

    Anyways, fantastic article: some real food for thought there. Keep it up! I look forward to more articles from this author!


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  18. First off, great set of articles :-)

    In the entire class vs attribute discussion I personally think that it’s more logical to use the class. It’s just a matter of “abstracting” the behaviour in the same way as we now abstract the presetation through the CSS. To me, writing maxlength=“300” is about the same as writing a .red, .blew, .green, etcetera CSS class and applying them at random.

    I think that you need to separate the behaviour based on “what it is”, not on “what it should do”, exactly like we define CSS based on “what it is” (i.e. header) and not “what it should look like” (i.e. red, center). The most appropriate solution to me would be to simply have a <textarea class=“message”> and then define somewhere else how a messae textbox looks (CSS) and how it should behave (JS).

    This means that in my mind, values such as the maxlength should be put in the JS script or in a separate file/definition the JS reads from, and not in the (X)HTML markup.

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  19. I’ve marvelled at many of the articles at ALA, and I agree it’s up to any individual designer to press the limits. My only annnoyance here is that ALA has been a champion of ‘standards’ yet when I follow the link to the quirksmode site, it doesn’t recognise firefox, and so I have to view a java-free version of the site. Not standards friendly – from the start. Then, on the browser page, no mention of firefox? What of these 25 million new users? I have no doubt that quirks’ owner is a brilliant programmer/designer etc etc, but this is not doing std comp any favours. Love tips/tricks etc, but in the scheme of things, this article is not much better than an article on some MS proprietory easter eggery – until “standards” catch up. Is ALA now hoping to do what MS did and champion buggy and restrictive, limited access techniques for delivering ‘cool’ content to those who are dumb enough (in a bug infested world) to enable java everything – for the sake of viewing ‘cool’ sites. Btw, I not only had to view an ugly “quirks.. site doesn’t support your browser” 404 style page, but it didn’t even auto-redirect. Not a good look. In ALA’s best defence, this is the first article where I feel ALA may have ‘jumped the shark’. (jump the shark: episode of Happy Days where Fonzy goes to Florida and daredevil style, ski-jumps over a killer shark – 2 part episode.. ratings fell immediately. Keep it real. This article can only add fuel to the fire that is the argument that: code-freaks will always find a way to break things and in doing so, make arguments for MS to fix us up.

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  20. A Soul asked:

    >Is ALA now hoping to do what MS did and champion buggy and restrictive, limited access techniques for delivering ‘cool’ content to those who are dumb enough (in a bug infested world) to enable java everything – for the sake of viewing ‘cool’ sites.


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  21. For certain behaviors, I’ve used this technique.  I also like it for validation triggered as you go (via onchange) rather than onsubmit.

    But for validation triggered from onsubmit, it doesn’t scale and I don’t like how I’m forced to maintain it.  After a form gets sufficiently complex, putting the validation parameters within each element becomes difficult to manage and support.  It is much easier, in my experience, to clump all of your validation code together within a single function, even if it means that removing a field now means to have to do it twice (once in the HTML, once in the validation script).  This becomes even more important when you have interconditional validation such as “If Status is not draft and Time_Sensitive is checked then make sure the estimated date is populated, valid, and, if marked as high priority, also within the next two weeks.”

    I’ve finally settled on a standard validation script library ( ) and love it (except that I’ve yet to get around to integrating overlib instead of an ugly alert box).

    By the way, a related link you might find interesting mixing presentation with validation by changing the css class name from “RequiredField” to “ValidField” in the onchange: Mixing that idea with this article would have some potential.

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  22. >yet when I follow the link to the quirksmode
    >site, it doesn’t recognise firefox,

    Why should it have to recognize Firefox? Any site should work in any browser (and mine does).

    >and so I have to view a java-free version of >the site.

    My site is guaranteed 100% Java free because I don’t have the faintest idea how to write Java. Therefore every visitor sees the Java-free version.

    JavaScript is another matter, of course. If your browser doesn’t support the W3C DOM it doesn’t get the JavaScript interface.

    >Then, on the browser page, no mention of >firefox?  What of these 25 million new users?

    It mentions Firefox’s parent browser rather a lot, and with lots of details. You do need to know just the tiniest bit about browsers, though.

    >I not only had to view an ugly “
    >doesn’t support your browser” 404 style page,

    That’s not what the page says. Please read again.

    >but it didn’t even auto-redirect.

    Where should it redirect to? Isn’t it better to give the visitor a choice of destinations?

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  23. >but it didn’t even auto-redirect.

    Good response PPK. Excuse my overuse of metaphors, but redirecting someone in a situation like that would be the equivalent of you driving someone out to the middle of nowhere when they asked you for directions.

    I had a thought about getting around the whole validation problem thing. The only solution to use custom attribues WITHOUT any sort of DTD and to have the page validate is, well, there is none. It’s called a “tradeoff”. We have a lot of them (fixed vs fluid-width, text/html vs application/xhtml+xml, etc). I’m suprised so many developers aren’t used to them by now.

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  24. For what it’s worth, to you probably not a lot, but to my clients a good chunk of change :), I thought I’d add my thoughts.

    To start with let me thank PPK and all of you who have taken the time to contribute to this discussion.  Not only has this article and comments been informative, but genuinely entertaining to think about.  It’s these kinds of issues that make web design and development so interesting to me.

    Let me also say that, like many developers, I strive for standards compliant design and development, but occasionally make non-compliant choices (or I should say compliance with older standards) brought on by the reality of today’s browsers.  Even the great Eric Meyers, CSS guru, uses a table for the basic layout of his examples in his books. gasp  However he strives for CSS usage in all other ways.

    So I’ve decided on the following path for myself:

    1. I’m going to add one additional attribute to my HTML elements, behavior.  I think this will add the least and get me the most.

    2. I’m going to keep my values for this attribute as simple as possible.  This is how I make my values for the class attribute.

    3. I think I need different “groupings” for presentational and behavioral.  For example, I want to display form elements in a single form in a consistent manner, but I want to validate email addresses in forms in a consistent way across pages in an application.  I think the combination of IDs, classes, and “behaviors” will give me all the hooks I need to handle the situations I’ve seen presented here and reduce redundancy in my code.

    4. I think this will keep my JavaScript as simple, clean and atomic as possible.

    5. I don’t have a problem with a custom DTD.

    6. I want to keep the details of my behaviors external to my structure.  For me I’ve decided to keep these details in my JavaScript file.  The reason I went with this as opposed to external XML files, etc, is again to keep my JavaScript and other code as simple as possible.

    So there it is.  My “centrist?” view of the ideas presented here.

    Thanks again for providing a space for and participating in this discussion.  It’s been very useful for me.


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  25. Very often I find myself using a class I’ve written in PHP to generate forms dynamically, by which I mean, you can generate the forms from any database table without prior knowledge of what the table structure is. It is aware of the field lengths in the database and so for input elements it can dynamically include the maxlength attribute.

    For me this answers the question of whether maxlength information should be considered structural or behavioural: it just doesn’t matter. There just is no other good place to put the information except in the XHTML file when it is generated, either using element attributes or (as someone else suggested) inside a comment near the element.

    I have no problem thinking that the requirements of form fields are structural. What you end up doing when a user breaks the constraints is behavioural. In fact I’d go so far as to say that the choice bewteen textarea and input is more presentational than structural, whereas the validation requirements of the field are more structural than behavioural. The lack of maxlength attribute for textareas is an oversight. But that’s just my take.

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  26. I love the idea of using custom attributes.  I’ve used classes to achieve this sort of thing in the past, and like the idea of using attributes for this purpose.

    The only thing I might add is the use of namespaces to use attributes within my own namespace.  For example js:required as opposed to just required.  This would clearly call out that the attribute isn’t defined by XHTML, rather some names space called js.  Namespaces in XML is a w3c standard:

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  28. Why not just perform a match on the Name of the text field?  For instance, I use an onload=init() for the body that searches through all of the input tags that are type=text and adds onblur=validateDate(this) if the name of the text field contains ‘Date’.  I do something similar for ‘Phone’ and pretty much anything else I need to validate.

    I can also use the same code to add any number of classes to any or all of the text fields.  That way all the structure has to have is “<input type=text name=xyzDate>” and onload javascript attaches both presentation AND behavior so changing either requires absolutely NO changes to the structure.

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  29. I’ve been following this debate (and the larger debate on over structure vs. presentation.

    I have to say that part of me that wants things to be logical and efficient leans toward defining my web pages semantically, and then using CSS to control layout and design.

    However, the realist in me knows that this is a practical impossibility. Anyone that has designed a slightly complex website – especially one that involves variable formatting between pages – knows that writing perfectly semantically driven code is impossible. We always end up making little compromises to get our layout to work right. stuff like <div class=“clear”></div>
    is not semantic – but sometimes its the only way to deal with floated columns. Look at the code for this website – try and argue that its semantic not presentational! If, a magazine which is dealing with very spefic and predicable data chunks and consistent presentation, can’t write semanic code who can?

    The funniest thing is that we can kill ourselves designing these perfectly defined documents, but don’t all websites designed this way tend to end up looking very similar? Why? because if we design our documents semantically we lose a lot of layout flexibility. We can use CSS to achieve complex designs that look even better than table based designs – but websites designed this way are never defined semantically – and never will be, because at the end of the day, web pages are presentational documents. We don’t see similar arguments in the print layout community for semantically designed documents – so why in the web design community?

    I think the larger debate is an interesting one, but that in truth it applies to only a small subset of website applications, such as content management systems; and that even within this small subset of applications there is a lot or room for flexibility in how one strikes a balance between semantic logic and presentational necessitates.

    For MOST websites, none of this should be a concern. We can argue all we want if maxlength=200 is presentational or structural, and those people that design websites with the maxlength=200 hidden somewhere deep in the JavaScript because they have a firmly rooted ideological belief that it is structural not presentational – bring me a website that has no <div class=”clearboths”><div>’s I’ll be very impressed – but more surprised.

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  30. Justin, your point is well made and quite on target, however, it is possible to make completely semantic sites and then, via JavaScript, add not only the behaviours, but also any “presentational” elements such as the divs you mentioned.

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