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Dynamic CSS and JS loading

DHTML

Dynamic CSS and JS loading

by  dkdude  Posted    (Edited  )
This is one way of loading dynamic CSS and JS. It takes a few files to complete my example, but they all rely on the [tt]loader.js[/tt].

Here we go ...

Let look at at basic xhtml document with a few [color red]extensions[/color]:

[tt]index.html[/tt]

Code: 
[b]<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
  <title>Dynamic Script &amp Style Loader</title>
  <meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1" />
  <link type="text/css" rel="stylesheet" href="[color red]baseline.css[/color]" />
  <script type="text/javascript" src="[color red]generic.js[/color]"></script>
  <script type="text/javascript" src="[color red]loader.js[/color]"></script>
  <script type="text/javascript" src="[color red]debug.js[/color]"></script>
</head>
  <body>
    <h3>
      My Dynamic Script &amp; Style Loader
    </h3>
    <hr />
    <h4>Let's change styles!</h4>
    <p>
      <button onclick="load_stylesheet('[color red]verdana.css[/color]')">
        Load the verdana.css stylesheet
      </button>
      <br />
      <button onclick="load_stylesheet('[color red]arial.css[/color]')">
        Load the arial.css stylesheet
      </button>
      <br />
      <button onclick="load_stylesheet('[color red]impact.css[/color]')">
        Load the impact.css stylesheet
      </button>
    </p>
    <hr />
    <h4>
      We can change scripts too!
    </h4>
    <p>
      <button onclick="hello()" id="myButton">
        I say &quot;Hello world!!&quot;
      </button>
      <br />
      <button onclick="load_script('[color red]hello.js[/color]')">
        Change the function of that button &nbsp; <b>&uarr;</b>
      </button>
    </p>
    <hr />
    <button onclick="[color red]stat()[/color]">
      Watch the Dynamic Load History
    </button>
  </body>
</html>[/b]

The document has a baseline-styling for the buttons:

[tt]baseline.css[/tt]
Code: 
[b]body {
  text-align	: center;
}

button {
  width		: 300px;
  padding		: 5px;
  margin		: 10px;
}[/b]

This is quite basic xhtml. And this document uses a few JavaScript extensions.

One is a gereric "hello world" script (which we will be replacing dynamically):

[tt]generic.js[/tt]

Code: 
[color gray]//---------------------------------------------------------------------------
//    The classic 'Hello World' :
//---------------------------------------------------------------------------[/color][b]
function hello() {
  alert('Hello world!!');
}
[/b]

Now, let's have a look at the actual Script & Stylesheet loader :

[tt]loader.js[/tt]
Code: 
[color gray]//---------------------------------------------------------------------------
//    Check to see if dubugging is enabled :
//---------------------------------------------------------------------------
[/color][b]if(!eval(debug)==true)
  var debug = false;;


[/b][color gray]//---------------------------------------------------------------------------
//    Let's load some JavaScripts :
//---------------------------------------------------------------------------
[/color][b]function load_script(filename) {
  var script = document.createElement('script'); 
  script.type = 'text/javascript'; 
  script.src = filename; 
  document.getElementsByTagName('head')[0].appendChild(script);
  if(debug)
    monitor(dynScripts, filename);
}


[/b][color gray]//---------------------------------------------------------------------------
//    Let's load some Stylesheets :
//---------------------------------------------------------------------------
[/color][b]function load_stylesheet(filename) {
  var css = document.createElement('link'); 
  css.rel = 'stylesheet'; 
  css.type = 'text/css'; 
  css.href = filename; 
  document.body.appendChild(css);
  if(debug)
    monitor(dynStyles, filename);
}


[/b][color gray]//---------------------------------------------------------------------------
//    Watch the status - IF enabled :
//---------------------------------------------------------------------------
[/color][b]function stat() {
  [/b][color gray]// IF debugging is enabled, then dump via the dynStatus() function :[/color][b]
  if(debug)
    dynStatus();
  [/b][color gray]// ELSE say that debugging is disabled ::[/color][b]
  else
    alert('Debug not enabled');
}
[/b]

Here's the three sample stylesheets that are (or can be) dynamic loaded:

[tt]verdana.css[/tt]

Code: 
[b]h3 {
  font-family           : verdana;
  font-size             : 22px;
  font-weight           : bold;
  color                 : #202020;
  letter-spacing        : 5px;
}

body {
  background-color      : #7DA177;
}[/b]

[tt]arial.css[/tt]

Code: 
[b]h3 {
  font-family           : arial;
  font-size             : 22px;
  font-weight           : bold;
  color                 : #EAEAEA;
  letter-spacing        : 5px;
}

body {
  background-color      : #4B6697;
}[/b]

and fianlly [tt]impact.css[/tt]

Code: 
[b]h3 {
  font-family           : impact;
  font-size             : 22px;
  font-weight           : normal;
  color                 : #404040;
  letter-spacing        : 5px;
}

body {
  background-color      : #F8E488;
}[/b]

Now, let's replace the generic hello world message:

[tt]hello.js[/tt]

Code: 
[color gray]//---------------------------------------------------------------------------
//    Fetch the button that's about to change function :
//---------------------------------------------------------------------------
[/color][b]var myButton = document.getElementById('myButton');


[/b][color gray]//---------------------------------------------------------------------------
//    Change the label of it :
//---------------------------------------------------------------------------
[/color][b]myButton.innerHTML = 'I now say &quot;Hello YOU!!&quot;';


[/b][color gray]//---------------------------------------------------------------------------
//    Change the background-color of it :
//---------------------------------------------------------------------------
[/color][b]myButton.style.backgroundColor = '#000000';


[/b][color gray]//---------------------------------------------------------------------------
//    Change the text color of it :
//---------------------------------------------------------------------------
[/color][b]myButton.style.color = '#EAEAEA';


[/b][color gray]//---------------------------------------------------------------------------
//    Change the font-weight of it :
//---------------------------------------------------------------------------
[/color][b]myButton.style.fontWeight = 'bold';


[/b][color gray]//---------------------------------------------------------------------------
//    Replacement hello() message for the button :
//---------------------------------------------------------------------------
[/color][b]function hello() {
  alert('Hello YOU!!');
}[/b]

Finally, as an option, you can include the debugger (like in my example index.html):

[tt]debug.js[/tt]

Code: 
[color gray]//---------------------------------------------------------------------------
// Global debugging variable :
//---------------------------------------------------------------------------
[/color][b]var debug = true;


[/b][color gray]//---------------------------------------------------------------------------
// Global Dynamic Script Name Monitor Array :
//---------------------------------------------------------------------------
[/color][b]var dynScripts = new Array();


[/b][color gray]//---------------------------------------------------------------------------
// Let's add a label to it :
//---------------------------------------------------------------------------
[/color][b]dynScripts[0] = '\n\nDynamic Scripts History:\n====================';


[/b][color gray]//---------------------------------------------------------------------------
// Global Dynamic Stylesheet Name Monitor Array :
//---------------------------------------------------------------------------
[/color][b]var dynStyles = new Array();


[/b][color gray]//---------------------------------------------------------------------------
// Let's add a label to it :
//---------------------------------------------------------------------------
[/color][b]dynStyles[0] = 'Dynamic Styles History:\n====================';


[/b][color gray]//---------------------------------------------------------------------------
// Log the loaded module names :
//---------------------------------------------------------------------------
[/color][b]function monitor(myArray, value) {
  var next = myArray.length;
  myArray[next] = value;
}


[/b][color gray]//---------------------------------------------------------------------------
// Alert the status - IF debugging is enabled :
//---------------------------------------------------------------------------
[/color][b]function dynStatus() {
  [/b][color gray]// Split array elements into seperate lines :[/color][b]
  var output = dynStyles.concat(dynScripts).join('\n');
  alert(output);
}[/b]

Hope you find this FAQ useful ...

Happy coding!
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