Requiring JavaScript
Some advanced web applications would not be possible without JavaScript. Both Section 508 and WCAG 2.0 allow JavaScript to be required so long as the JavaScript content and interactions are compliant and accessible. Whether you should require JavaScript is not really an accessibility question. It is a general usability question. Some users (most users indicate less than 2%), regardless of disability, may have JavaScript disabled. When possible, the functionality should be available without requiring JavaScript. When this is not possible, the functionality should fail gracefully (i.e., inform the user that JavaScript is required).
It is a common misconception that screen readers to not support JavaScript or that users with disabilities always disable JavaScript. The approach to accessibility is then to only ensure that the non-JavaScript version or fallback content is accessible. A screen reader user survey found that 98.6% of respondents had JavaScript enabled, meaning that in this case, nearly all screen reader users would not get the accessible fallback but would instead get the inaccessible scripted content. In order to be compliant and accessible, all scripted content and functionality must be accessible.
