A fix for the iOS orientationchange zoom bug.

ios-orientation-fix.js

/*! A fix for the iOS orientationchange zoom bug.
 Script by @scottjehl, rebound by @wilto.
 MIT / GPLv2 License.
*/
(function(w){
       
        // This fix addresses an iOS bug, so return early if the UA claims it's something else.
        var ua = navigator.userAgent;
        if( !( /iPhone|iPad|iPod/.test( navigator.platform ) && /OS [1-5]_[0-9_]* like Mac OS X/i.test(ua) && ua.indexOf( "AppleWebKit" ) > -1 ) ){
                return;
        }
 
    var doc = w.document;
 
    if( !doc.querySelector ){ return; }
 
    var meta = doc.querySelector( "meta[name=viewport]" ),
        initialContent = meta && meta.getAttribute( "content" ),
        disabledZoom = initialContent + ",maximum-scale=1",
        enabledZoom = initialContent + ",maximum-scale=10",
        enabled = true,
                x, y, z, aig;
 
    if( !meta ){ return; }
 
    function restoreZoom(){
        meta.setAttribute( "content", enabledZoom );
        enabled = true;
    }
 
    function disableZoom(){
        meta.setAttribute( "content", disabledZoom );
        enabled = false;
    }
       
    function checkTilt( e ){
                aig = e.accelerationIncludingGravity;
                x = Math.abs( aig.x );
                y = Math.abs( aig.y );
                z = Math.abs( aig.z );
                               
                // If portrait orientation and in one of the danger zones
        if( (!w.orientation || w.orientation === 180) && ( x > 7 || ( ( z > 6 && y < 8 || z < 8 && y > 6 ) && x > 5 ) ) ){
                        if( enabled ){
                                disableZoom();
                        }              
        }
                else if( !enabled ){
                        restoreZoom();
        }
    }
       
        w.addEventListener( "orientationchange", restoreZoom, false );
        w.addEventListener( "devicemotion", checkTilt, false );
 
})( this );