Example of Browser Sniffing Gone Bad

browser-sniffing.js

// Example of browser sniffing gone bad
var ieMatch = navigator.userAgent.match( /MSIE\s(\d)/ );
if ( ieMatch && parseInt( ieMatch[ 1 ], 10 ) >= 8 ) {
  console.log( "IE 8+" );
} else {
  console.log( "Feature Not Supported" );
}

feature-detection.js

// Prefered technique of determining feature support
if ( Modernizr.geolocation ) {
  // Find the user's current location...
} else {
  // Provide some sort of polyfill
}