ios-viewport-scaling-bug-fix-original.js

// Original code from http://www.blog.highub.com/mobile-2/a-fix-for-iphone-viewport-scale-bug/

var metas = document.getElementsByTagName('meta');
var i;
if (navigator.userAgent.match(/iPhone/i)) {
	for (i=0; i<metas.length; i++) {
		if (metas[i].name == "viewport") {
			metas[i].content = "width=device-width, minimum-scale=1.0, maximum-scale=1.0";
		}
	}
	document.getElementsByTagName('body')[0].addEventListener("gesturestart", gestureStart, false);
}
function gestureStart() {
	for (i=0; i<metas.length; i++) {
		if (metas[i].name == "viewport") {
			metas[i].content = "width=device-width, minimum-scale=0.25, maximum-scale=1.6";
		}
	}
}

ios-viewport-scaling-bug-fix.js

// Rewritten version
// By @mathias, @cheeaun and @jdalton

(function(doc) {

	var addEvent = 'addEventListener',
	    type = 'gesturestart',
	    qsa = 'querySelectorAll',
	    scales = [1, 1],
	    meta = qsa in doc ? doc[qsa]('meta[name=viewport]') : [];

	function fix() {
		meta.content = 'width=device-width,minimum-scale=' + scales[0] + ',maximum-scale=' + scales[1];
		doc.removeEventListener(type, fix, true);
	}

	if ((meta = meta[meta.length - 1]) && addEvent in doc) {
		fix();
		scales = [.25, 1.6];
		doc[addEvent](type, fix, true);
	}

}(document));