The Guardian's Lightweight Modernizr Replacement

browsercheck.js

function isModernBrowser() {
  return 'querySelector' in document && 
    'addEventListener' in window && 
    'localStorage' in window && 
    'sessionStorage' in window && 
    (('XMLHttpRequest' in window && 
     'withCredentials' in new XMLHttpRequest()) || 
    'XDomainRequest' in window);
}