Accessibility is an aspect of web development that is often overlooked. I would argue that it is as vital as overall performance and code reusability. We justify our endless pursuit of better performance and responsive design by citing the users, but ultimately these pursuits are done with the user's device in mind, not the user themselves and their potential disabilities or restrictions.
A responsive app should be one that delivers its content based on the needs of the user, not only their device.
Luckily, there are tools to help alleviate the learning curve of accessibility-minded development. For example, GitHub recently released their accessibility error scanner, AccessibilityJS and Deque has aXe. This article will focus on a different one: Ally.js, a library simplifying certain accessibility features, functions, and behaviors.
Modaal is a WCAG 2.0 Level AA accessible modal window plugin.
Modals seem so hard to get right from an accessibility perspective, I'm not proud to say I've never tried. Something like moving focus to the modal when it opens and moving focus back to where it was when the modal closes seems like a particularly tricky thing to get right.