Modernizr position fixed check

modernizr.positionfixed.js

;(function(Modernizr, window) {
    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);
        }
   
        return ret;
    });
    
    Modernizr.addTest('iospositionfixed', function () {
        var test  = document.createElement('div'),
            ret,
            fake = false,
            root = document.body || (function () {
                fake = true;
                return document.documentElement.appendChild(document.createElement('body'));
            }());
        
        if (typeof document.body.scrollIntoViewIfNeeded === 'function') {
        
            var oldCssText = root.style.cssText,
                testScrollTop = 20,
                originalScrollTop = window.pageYOffset;

            root.appendChild(test);

            test.style.cssText = 'position:fixed;top:0px;height:10px;';

            root.style.height="3000px";
            
            /* avoided hoisting for clarity */
            var testScroll = function() {
                if (ret === undefined) {
                    test.scrollIntoViewIfNeeded();
                    if (window.pageYOffset === testScrollTop) {
                        ret = true;
                    } else {
                        ret = false;
                    }
                }
                window.removeEventListener('scroll', testScroll, false);
            }

            window.addEventListener('scroll', testScrollTop, false);
            window.setTimeout(testScroll, 20); // ios 4 does'nt publish the scroll event on scrollto
            window.scrollTo(0, testScrollTop);
            testScroll();

            root.removeChild(test);
            root.style.cssText = oldCssText;
            window.scrollTo(0, originalScrollTop);

        } else {
            ret = Modernizr.positionfixed; // firefox and IE doesnt have document.body.scrollIntoViewIfNeeded, so we test with the original modernizr test
        }
            
        if (fake) {
            document.documentElement.removeChild(root);
        }

        return ret;
    });
})(Modernizr, window);

Hi @jtangelder.

It's worth noting that it looks as though with the recent release of OS 10 the UA string will match the regex ua.match(/(iphone|ipad|ipod).+(OS [0-4])/i) eg iPhone OS 10_3_1