This is a small method to do the somewhat complicated job of figuring out whether a browser is operating in high contrast mode. The end goal is to be able to style the page differently so these users.
This works on all Windows browsers but only Firefox on Mac. The way this works is by detecting when the browser's computed styles are different than the given ones. In Windows, the high contrast theme coerces the browsers to ignore a website's given styles in favor of its own. In OSX, the system level high contrast settings will alter the entire display at a lower level so browsers won't be aware of it and therefore neither will we. Firefox has options in the content pane of preferences to ignore website's styles and will behave similarly to Windows at that point. The likelihood of Apple changing their approach anytime soon is probably small.
var checkHighContrast = require('checkHighContrast');
if( checkHighContrast(body) ) {
// ... setup alternative styles here ...
}