Custom Modernizr tests that are useful.

modernizr-tests.js

/* modernizr-test.js
 * Daniel Ott
 * 3 March 2011
 * Custom Tests using Modernizr's addTest API
 */

/* iOS
 * There may be times when we need a quick way to reference whether iOS is in play or not.
 * While a primative means, will be helpful for that.
 */
Modernizr.addTest('ipad', function () {
  return !!navigator.userAgent.match(/iPad/i);
});

Modernizr.addTest('iphone', function () {
  return !!navigator.userAgent.match(/iPhone/i);
});

Modernizr.addTest('ipod', function () {
  return !!navigator.userAgent.match(/iPod/i);
});

Modernizr.addTest('appleios', function () {
  return (Modernizr.ipad || Modernizr.ipod || Modernizr.iphone);
});

/* CSS position:fixed
 * Not supported in older IE browsers, nor on Apple's iOS devices.
 * Actually the token example on the Modernizr docs. http://www.modernizr.com/docs/
 */
Modernizr.addTest('positionfixed', function () {
    var test    = document.createElement('div'),
        control = test.cloneNode(false),
        fake = false,
        root = document.body || (function () {
            fake = true;
            return document.documentElement.appendChild(document.createElement('body'));
        }());

    var oldCssText = root.style.cssText;
    root.style.cssText = 'padding:0;margin:0';
    test.style.cssText = 'position:fixed;top:42px'; 
    root.appendChild(test);
    root.appendChild(control);
    
    var ret = test.offsetTop !== control.offsetTop;

    root.removeChild(test);
    root.removeChild(control);
    root.style.cssText = oldCssText;
    
    if (fake) {
        document.documentElement.removeChild(root);
    }
    
    /* Uh-oh. iOS would return a false positive here.
     * If it's about to return true, we'll explicitly test for known iOS User Agent strings.
     * "UA Sniffing is bad practice" you say. Agreeable, but sadly this feature has made it to
     * Modernizr's list of undectables, so we're reduced to having to use this. */
    return ret && !Modernizr.appleios;
});

But...but...but...!

Modernizr.appleios isn't sufficient, since ios5+ incorporates (true) position fixed.

See the famous threads: Modernizr/Modernizr#167 and Modernizr/Modernizr#539

But as a gist this is a nice reference doc that could be increased.

For determining mobile see: http://stackoverflow.com/questions/16279522/yepnope-modernizr-screen-width-conditions

Basically:
{
test: Modernizr.mq('all and (max-width: 1070px)'),
}

These tests are outdated in 2015. Simply relying on the UserAgent String isn't enough since Microsoft injected the word iPhone in IE user agent. https://msdn.microsoft.com/en-us/library/hh869301(v=vs.85).aspx (look for the word iPhone)