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Javascript Events: Getting notified of changes in an control value

I have the following problem:

I have an HTML textbox (<input type="text">) whose contents are modified by a script I cannot touch (it is my page, but i’m using external components).

I want to be notified in my script every time the value of that textbox changes, so I can react to it.

I’ve tried this:

txtStartDate.observe('change', function() { alert('change' +  txtStartDate.value) });

which (predictably) doesn’t work. It only gets executed if I myself change the textbox value with the keyboard and then move the focus elsewhere, but it doesn’t get executed if the script changes the value.

Is there another event I can listen to, that i’m not aware of?



I’m using the Prototype library, and in case it’s relevant, the external component modifying the textbox value is Basic Date Picker (www.basicdatepicker.com)

Answer

As you’ve implied, change (and other events) only fire when the user takes some action. A script modifying things won’t fire any events. Your only solution is to find some hook into the control that you can hook up to your listener.

Here is how I would do it:

basicDatePicker.selectDate = basicDatePicker.selectDate.wrap(function(orig,year,month,day,hide) {
  myListener(year,month,day);
  return orig(year,month,day,hide);
});

That’s based on a cursory look with Firebug (I’m not familiar with the component). If there are other ways of selecting a date, then you’ll need to wrap those methods as well.

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Is D a credible alternative to Java and C++? [closed]

Is the D language a credible alternative to Java and C++? What will it take to become a credible alternative? Should I bother learning it? Does it deserve evangelizing?

The main reason I ask is that with the new C++ standard (c++0x) almost here, it’s clear to me that the language has gone well past the point of no return with respect to anyone ever understanding it. I know that C/C++ will never die but at some point we need to move on. Even COBOL had its day and Java has in many respects undone C++. So what’s next? Does D fill the bill?

Answer

What determines the success and popularity of a programming language for real-world software development is only partially related to the quality of the language itself. As a pure language, D arguably has many advantages over C++ and Java. At the very least it is a credible alternative as a pure language, all other things being equal.

However, other things matter for software development – almost more than the language itself: portability (how many platforms does it run on), debugger support, IDE support, standard library quality, dynamic library support, bindings for common APIs, documentation, the developer community, momentum, and commercial support, just to name a few. In every one of those regards, D is hopelessly behind Java, C++, and C#. In fact, I’d argue it’s even behind so-called “scripting” languages like Python, Perl, PHP, Ruby, and even JavaScript in these regards.

To be blunt, you simply can’t build a large-scale, cross-platform application using D. With an immature standard library, no support in any modern IDEs (there are plugins for both Visual Studio and Xamarin Studio/MonoDevelop), limited dynamic/shared library support, and few bindings to other languages, D is simply not an option today.

If you like what you see of D, by all means, learn it – it shouldn’t take long if you already know Java and C++. I don’t think evangelism would be helpful – at this point if D is going to succeed, what it really needs is more people quietly using it and addressing its major shortcomings like standard library and IDE support.

Finally, as for C++, while most agree the language is too complex, thousands of companies are successfully using C++ as part of a healthy mix of languages by allowing only a smaller, well-defined subset of the language. It’s still hard to beat C++ when both raw performance and small memory usage are required.

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How do I get a floating footer to stick to the bottom of the viewport in IE 6?

I know this would be easy with position:fixed, but unfortanately I’m stuck with supporting IE 6. How can I do this? I would rather use CSS to be clean, but if I have to use Javascript, that’s not the end of the world. In my current implementation I have a “floating footer” that floats above the main content area and is positioned with Javascript. The implementation I have right now is not particular elegant even with the Javascript, so my questions are:

  1. Is there a way to do this without Javascript?
  2. If I have to use Javascript, are there any “nice” solutions to this floating footer problem? By “nice” I mean something that will work across browsers, doesn’t overload the browser’s resources (since it will have to recalculate often), and is elegant/easy to use (i.e. it would be nice to write something like new FloatingFooter("floatingDiv")).

I’m going to guess there is no super easy solution that has everything above, but something I can build off of would be great.

Finally, just a more general question. I know this problem is a big pain to solve, so what are other UI alternatives rather than having footer content at the bottom of every page? On my particular site, I use it to show transitions between steps. Are there other ways I could do this?

Answer

This may work for you. It works on IE6 and Firefox 2.0.0.17 for me. Give it a shot. I made the footer’s height very tall, just for effect. You would obviously change it to what you need. I hope this works for you.

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>Liquid Footer</title>
    <style type="text/css">
    .footer {
background-color: #cdcdcd;
height: 180px;
text-align: center;
font-size:10px;
color:#CC0000;
font-family:Verdana;
padding-top: 10px;
width: 100%;
position:fixed;
left: 0px;
bottom: 0px;
}
    </style>
    <!--[if lte IE 6]>
    <style type="text/css">
    body {height:100%; overflow-y:auto;}
    html {overflow-x:auto; overflow-y:hidden;}
    * html .footer {position:absolute;}
    </style>
    <![endif]-->
</head>

<body>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
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   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   This is to expand the content on the page<br>
   <div class="footer">-- This is your liquid footer --</div>
</body>
</html>

Categories
discuss

Why is the Java main method static?

The method signature of a Java mainmethod is:

public static void main(String[] args) {
    ...
}

Is there a reason why this method must be static?

Answer

The method is static because otherwise there would be ambiguity: which constructor should be called? Especially if your class looks like this:

public class JavaClass{
  protected JavaClass(int x){}
  public void main(String[] args){
  }
}

Should the JVM call new JavaClass(int)? What should it pass for x?

If not, should the JVM instantiate JavaClass without running any constructor method? I think it shouldn’t, because that will special-case your entire class – sometimes you have an instance that hasn’t been initialized, and you have to check for it in every method that could be called.

There are just too many edge cases and ambiguities for it to make sense for the JVM to have to instantiate a class before the entry point is called. That’s why main is static.

I have no idea why main is always marked public though.

Categories
discuss

Best Java/Swing browser component? [closed]

What’s the best cross platform Java Swing browser component at least able to play nicely in a swing interface (lightweight component ?) and able to run on MacOSX and Windows ?

Things like : FlyingSaucer, JDIC, maybe others ?

Answer

i belive this could help:

http://djproject.sourceforge.net/ns/index.html

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