Question

How do I check (using Java or JavaScript) if a browser has support for blind or partially-sighted people?

Answer 1

If you are looking to determine whether an assistive technology (like JAWS or Window-Eyes) are installed, no, you cannot with Javascript. These technologies use OS-level APIs, and current browsers don’t do anything that would cause their presence to be detectable. There is a flash-based hack that can detect newer versions of screen readers see http://webaim.org/techniques/flash/techniques

Perhaps you want to provide a different Flash interface or options if a user is using a screen reader. For instance, you may want to provide additional buttons or turn on self-voicing features when the person watching your movie is using a screen reader. You can detect screen readers using ActionScript. The Accessibility.isActive() function will return “true” if a screen reader that is capable of accessing Flash content is detected (currently only up-to-date versions of Window-Eyes, JAWS, and IBM Home Page Reader). For instance, you might add:

if (Accessibility.isActive()) { 
_root.selfVoicing.play(); 
}

Important
Because there is a slight delay between when your movie begins and when the screen reader is detected, Accessibility.isActive() may incorrectly return false during the first few moments that your movie is playing. The Flash movie must also have focus in order for this to work. This can be solved by associating the ActionScript with a button within the Flash movie.
Finally, this method of detecting a screen reader, will not detect all screen readers. It will only detect the most recent versions of screen readers that support MSAA and have the Flash 6+ player installed.
This method is the only way of automatically detecting screen readers on the web. If you want to provide alternative content for screen reader users, you could use a Flash movie to detect the presence of a screen reader and redirect appropriately. However, this also assumes that the user has the Flash player installed (which most users do). If the user does not have Flash, then the detection will not work and the user might be presented with additional accessibility issues. Care must also be taken in providing alternative content for screen reader users. The alternative content must be kept up-to-date and provide the same information and functionality as the non-screen reader content. Here is the code to redirect based on screen reader presence:

if (Accessibility.isActive()) { 
getURL(screenreaderpage.htm); 
} else { 
getURL(normalpage.htm); 
}