Replacing <noscript> with accessible, unobtrusive DOM/JavaScript

By Frank M. Palinkas · 29 Feb, 2008

Published in: accessibility, DOM, javascript, noscript, replace

Introduction

Peter-Paul Koch in his book "ppk on JavaScript", points out that the <noscript></noscript> element has a limitation. Modern user agents with JavaScript enabled will hide content contained within <noscript></noscript>, and reveal it when JavaScript is disabled. User agents that do not support JavaScript will display the content within it. User agents with partial/antiquated JavaScript capabilities however interpret the element correctly and do not show the content, but when JavaScript is disabled also do not show the content - it never gets seen. This has an impact on the accessibility of the content. If your writing is targeted at modern, standards-based, compliant, and fully capable JavaScript user agents, employing the <noscript> element is no problem. If the user agents among your audience are unpredictable, however, replacing the <noscript> element with another mechanism becomes significant. This article looks at one such solution.

You can download the code examples here, view the working code example here, or view and download the full project file here (click on the "Replacing <noscript> with Unobtrusive DOM/JavaScript" topic when you get there.)

The solution

So, how can the behavior intended by the <noscript> markup element be enabled in these antiquated/partially-capable JavaScript user agents? The workflow for my solution is as follows:

Insert an unobtrusive JavaScript "hook" via an id attribute value in the parent container's opening tag.
Associate the "hook" with an external JavaScript function, which sets up a parent-to-child relationship between the container and its content.
- When Javascript is enabled, the external function keeps the alternative content hidden.
- If the user agent cannot interpret the JavaScript expressions, the alternative content in the markup is revealed.
- When Javascript is disabled the function no longer works, and the alternative content in the markup is revealed. This ensures graceful degradation of the script.

Important Note: if the ability to hide the alternative content with JavaScript does not exist, the browser/user agent will be able to render the content ensuring accessibility and graceful degration.

Building the Markup

In this section you'll build up the markup portion of the example.

In the <head></head> element of the web page, insert a <script></script> element containing the path to the external noscript.js JavaScript file:
Create a <div></div> within the <body></body> element to contain the hidden content.
Give the opening tag of the <div> an id attribute with a value of "noscript", that is, <div id="noscript"> - this sets the unobtrusive hook to the external JavaScript function noscript().
Place all elements and content to be hidden while JavaScript is enabled within the <div id="noscript"></div> container.

The following web page markup sample illustrates this:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html lang="en">
<head>
  <title>noscript_example</title>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <script src="scripts/noscript.js" type="text/javascript"></script>
</head>
<body>
  <div id="noscript">
    <p>
      Lorem ipsum dolor sit amet, consectetuer adipiscing elit.
    </p>
    <ul>
      <li><a href="#">Hyperlink A</a></li>
      <li><a href="#">Hyperlink B</a></li>
    </ul>
  </div>
</body>
</html>

Building the unobtrusive DOM/JavaScript

In this section I'll take you through building up the two main sections of the JavaScript.

Writing the `if()` portion of the function

Between the if parentheses, place the document.removeChild expression - this tests to see if it is supported by the user agent.
- If it is supported the function will continue, and the div content will remain hidden.
- If it is not supported the function progresses to the else if() statement and tests it.
Declare the container div element and identify its id value as the external, unobtrusive "hook" to the markup.
Instruct the parent div to remove all child content within it.

Writing the `else if()` portion of the function

Between the else if parentheses, place the document.getElementById expression to test if it is supported by the user agent.
- If it is supported the function will continue, and the div content will remain hidden.
- If it is not supported the function will end, and the div content will be revealed, establishing graceful degradation of the script.
Return the element id where the style will be applied.
Set its style.display to "none" to control the presentation aspect of the child content.

The following script is contained in the noscript.js file, which is kept external, and linked to the web page as described in the "Building the Markup" section.

/* noscript.js */

 function addLoadEvent(func) {
    var oldonload = window.onload;
    if (typeof window.onload !== "function") {
        window.onload = func;
    } else {
        window.onload = function () {
            if (oldonload) {
                oldonload();
            }
            func();
        };
    }
 }
 var noscript = addLoadEvent(noscript);
 addLoadEvent(function () { 
 /* more code to run on page load */ 
 });
 
 function noscript()
 {
   if (document.removeChild)
     {
       var div = document.getElementById("noscript");
           div.parentNode.removeChild(div);
     }
   else if (document.getElementById)
     {
       document.getElementById("noscript").style.display = "none";
     }
 }

Summary

This article demonstrates a solution that replaces the <noscript></noscript> markup element with an external, unobtrusive JavaScript function. The noscript() function solves the problem that partially-capable/antiquated JavaScript user agents have with not revealing alternative content if JavaScript is disabled. Employing this function, they will reveal the content as intended. This ensures graceful degradation of the script, and full accessibility to the alternative content. Please feel free to comment on anything you think could be improved upon.

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