fixorientationzoom.js

/*
 An attempt at fixing the dreaded iOS orientationchange zoom bug http://adactio.com/journal/5088/. Seems to work!
 Authored by @scottjehl
 MIT License.
*/

(function(w){
	var doc = w.document;
  
	if( !doc.querySelectorAll ){ return; }

	var meta = doc.querySelectorAll( "meta[name=viewport]" )[ 0 ],
		initialContent = meta && meta.getAttribute( "content" ),
		disabledZoom = initialContent + ", maximum-scale=1.0",
		enabledZoom = initialContent + ", maximum-scale=10.0",
		enabled = true,
		orientation = w.orientation,
		rotation = 0;
  	
	if( !meta ){ return; }
  
	function restoreZoom(){
		meta.setAttribute( "content", enabledZoom );
		document.body.innerHTML = document.body.innerHTML;
		enabled = true;
	}
  
  	function disableZoom(){
		meta.setAttribute( "content", disabledZoom );
		enabled = false;
	}

	function checkTilt( e ){
		orientation = Math.abs( w.orientation );
		rotation = Math.abs( e.accelerationIncludingGravity.x );

		if( rotation > 8 && orientation === 0 ){
			if( enabled ){
				disableZoom();
			}	
		}
		else {
			if( !enabled ){
				restoreZoom();
			}
		}
		
	}

	w.addEventListener( "orientationchange", restoreZoom, false );
	w.addEventListener( "devicemotion", checkTilt, false );
  
})( this );